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Complex exudates in inflorescences of Vriesea species reveal evidence of lipophilic secretions by scales of bromeliads
... The presence of an oily secretion, for instance, is reported for many Vriesea species, and it was demonstrated that this secretion acts as a sticky trap for herbivores, effectively reducing damage in Vriesea bituminosa (Monteiro and Macedo 2014). Also, a study with three Vriesea species recently demonstrated that the scales in floral bracts can produce these oily secretions (Ballego-Campos et al. 2023). These findings provide new insight into the functional biology of bromeliad trichomes and call for a broader investigation of scales in the reproductive axis of Bromeliaceae. ...
... In light of the little knowledge regarding trichomes in inflorescences of bromeliads, as well as the recent discoveries regarding secretion in inflorescences of Tillandsioideae species (Ballego-Campos et al. 2020;Ballego-Campos et al. 2023), in this study, we investigated the presence of secretion in the floral bracts of 52 species of Tillandsioideae and 1 early-divergent bromeliad species, Brocchinia reducta Baker (Brocchinioideae). Our main goals were to investigate the presence and source of secretion in inflorescences, including the general nature of the exudate, and to describe the anatomy of floral bracts in the studied species, focusing on trichome structure and position. ...
... bituminosa, V. fenestralis and V. platynema var. rosea (see also Ballego-Campos et al. 2023). In species of Tillandsieae, a clear secretion was observed on the adaxial surface of bracts only in W. cyanea (Fig. 1J) and all studied Guzmania species (Table 1). ...
Bromeliaceae display many water-use strategies, from leaf impounding tanks to CAM photosynthesis and absorbing trichomes. Recent studies show that trichomes in inflorescences of bromeliads can exude viscous secretions, protecting against various stresses, including excessive water loss. In light of this, and considering the knowledge gap regarding inflorescence trichomes in bromeliads, we aimed to investigate the presence, source, and chemical nature of inflorescence secretions in species of the Tillandsioideae (Bromeliaceae) and to describe the anatomy of their floral bracts focusing on trichome structure and position.We conducted a prospection of secretory activity and anatomy in floral bracts in 52 species of Tillandsioideae and one early-divergent Bromeliaceae species. We used histochemical tests to investigate the presence and nature of secretion combined with standard light microscopy methods. Secretion appears in all studied species of tribe Vrieseeae, in Guzmania species, Wallisia cyanea, Tillandsia streptopylla (Tillandsieae), and Catopsis morreniana (Catopsideae). It is absent in Vriesea guttata (Vrieseeae), Racinaea crispa, and various Tillandsia species (Tillandsieae). Secretion is produced by peltate trichomes on the adaxial surface of young bracts and comprises hydrophilic and lipophilic substances. Bract anatomy revealed an internal mucilage-secreting tissue with wide distribution within subtribe Vrieseinae. Our results point to a broad occurrence of secretion associated with bracteal scales in inflorescences of Tillandsioideae. Secretory function is strongly related to trichomes of the adaxial surface, whereas the indumentum of the abaxial side is lacking or likely associated with water absorption; the latter case is especially related to small, xeric plants. Exudates might engage in colleter-like roles, protecting against desiccation, high-radiation, and herbivores. Directions for future research are presented.
... However, the lack of additional histochemical tests limits our analysis, since it may be mixed with other substances, such as lipids, for example, as already reported for mucilagesecreting peltate trichomes in inflorescences of Vriesea Lindley (1843: pl. 10) (Ballego-Campos et al. 2023). ...
A new species of Krenakanthus, a member of the bromelioid “Cryptanthoid complex”, is described based on plants discovered through collaborative citizen science. Krenakanthus ribeiranus and its only congener K. roseolilacinus are endemic to the “João Pinto Center of Biodiversity”, a still poorly explored region with Campos Rupestres and associated vegetation in the Rio Doce Valley, in eastern Minas Gerais state, Brazil. The unusual combination of morphological characters of K. ribeiranus, highlighted by plant delicacy and almost all leaf and flower parts covered by uniseriate, hair-like trichomes, is illustrated and discussed in comparison with K. roseolilacinus, including leaf and seed anatomy, as well as pollen morphology. This micro-endemic species is assessed as Critically Endangered, reinforcing the need for strategy to protect the biodiversity of the region. The morphology of the new species validates and strengthens the diagnostic flower characters used in the circumscription of Krenakanthus, suggesting as secondary diagnostic characters the habit, stature, and leaf conformation.
... In the studies by Ballego-Campos et al. (2020, anatomical and ultrastructural analyses showed that the mucilaginous secretion is produced by the wing cells. Ballego-Campos et al. (2023) studied three species of Vriesea sect. Xiphion (the same section of the V. oligantha complex) describing that the secretion from the scales is heterogeneous and contains hydrophilic and lipophilic substances, the latter can be lipids and/or terpenoids, or alkaloids, depending on the species. ...
The Vriesea oligantha complex comprises Vriesea lancifolia, Vriesea oligantha, and Vriesea pseudoligantha, which were recently transferred to Stigmatodon. Such species exhibit strong morphological convergence to live in rocky fields, which makes difficult their identification in the wild or in herbarium specimens. In a previous work, leaf characters helped in the species delimitation and evidenced a new taxon. Considering that morphology, anatomy, and aspects of floral biology can contribute to better define species limits and to indicate potential pollinators, individuals from nine populations of V. oligantha complex were comparatively studied. The typical V. oligantha is mainly distinguished by tubular flowers, with simple petal appendages and diurnal anthesis. The remaining individuals studied from different populations exhibit campanulate corollas, with denticulate petal appendages and nocturnal anthesis, not allowing for the separation of V. lancifolia, V. pseudoligantha, and a fourth taxon. Floral anatomy is less variable than the external morphology, with little contribution to the species delimitation; however, it is helpful in the circumscription of Stigmatodon. The infralocular septal nectaries and the floral features provide evidence that the main pollinators of campanulate and tubular flowers are bats and hummingbirds, respectively. Specific pollinator guilds in combination with fragmented populations may explain the limited gene flow amongst populations.
Capsule-type fruits are predominant in Bromeliaceae. However, the late divergent subfamily Bromelioideae generally presents fleshy fruits, which display a diverse range of morphologies even in related genera; however, there is almost no information regarding their anatomical and ontogenetic aspects. In this study we evaluate the fruit ontogeny of species from the major lineages of Bromelioideae, to better understand the possible paths in which fleshiness can be achieved in the subfamily. Flowers at pre-anthesis and anthesis, and fruits of Acanthostachys strobilacea, Billbergia pyramidalis, and Bromelia antiacantha were collected and processed with standard methods for analysis under light microscopy. Two basic ontogenetic pathways for achieving fleshiness were identified among the examined species. In the two former species, belonging to the core Bromelioideae, the pericarp development occurs solely through cell expansion and anticlinal cell division in the mesocarp. Conversely, in B. antiacantha, belonging to the tankless lineages, the pericarp development proceeds via both periclinal and anticlinal cell divisions of the outer and inner mesocarp. The analysis of fruit anatomy in the species included in this study highlights unprecedented traits of Bromelioideae fruits, such as the presence of the pericarp´s massive extra-carpellary portion in B. antiacantha, which contains many mucilage channels and fibrous tissue, and an intrusive septum in the carpellary portion, which acts as the main nutritive portion of the fruit. Additionally, in the present study, unique features of the ovary and the fruit, essential for characterizing the species were detailed, including the elongated placental tissue and the aliform projections of A. strobilacea. Our observations highlight distinct developmental processes to fleshy fruit formation in Bromelioideae. In this way, exploring the fruit ontogenetic diversity in Bromelioideae offers an exciting opportunity for future investigations. Besides, the unique fruit features identified bring out the importance of fruits as tools for genus delineation within this subfamily.
The legume tree Schizolobium parahyba from the Brazilian Atlantic Forest shows young aerial organs covered with a sticky exudate. Aiming to clarify the functional aspects of the sticky secretions, we performed analyses on the dynamics of secretion through the plant development and characterized the chemical nature of the exudates by histochemical tests. We also studied the secretory tissue using light and electron microscopy. The production of the exudates starts soon after seed germination, being evident in the epicotyl but not in the hypocotyl and cotyledons. The secretory activity extends throughout the juvenile and pre-reproductive phase, in primary stems and leaf portions. After the first flowering, secretion was no longer observed. The lipid exudates are secreted by the epidermis and are composed of mixtures of essential oils and oleoresins. Modified plastids, extensive rough endoplasmic reticulum, proliferated smooth endoplasmic reticulum, enlarged vacuoles containing flocculant materials, membrane debris, and convoluted tubules/lamellae membranes covered with osmiophilic deposits are the main features of the secretory epidermal cells. Secretion exits the protoplast by exocytosis and accumulates in the cuticle, resulting in a sheath of concentric bands of electron-dense deposits, and is released by cuticle peeling. The hydrophobic nature of the secretion, which forms an impermeable layer on the epidermis of young organs, is a relevant attribute of the aerial organs of S. parahyba. In addition to protecting against desiccation, this exudate effectively captures particles and immobilizes insects and other arthropods.
Buds of horse-chestnut trees are covered with a viscous fluid, which remains sticky after long-term exposure to heat, frost, radiation, precipitation, deposition of aerosols and particles, attacks by microbes and arthropods. The present study demonstrates that the secretion does not dry out under arid conditions, not melt at 50 °C, and not change significantly under UV radiation or frost at a microscopic level. It is slightly swellable under wet conditions; and, it universally wets and adheres to substrates having different polarities. Measured pull-off forces do not differ between hydrophilic and lipophilic surfaces, ranging between 58 and 186 mN, and resulting in an adhesive strength up to 204 kPa. The mechanical and chemical properties of secretion resemble those of pressure-sensitive adhesives. The Raman, infrared, and nuclear magnetic resonance spectra show the clear presence of saturated aliphatic hydrocarbons, esters, free carboxylic acids, as well as minor amounts of amides and aromatic compounds. We suggest a multi-component material (aliphatic hydrocarbon resin), including alkanes, fatty acids, amides, and tackifying terpenoids embedded in a fluid matrix (fatty acids) comprising nonpolar and polar portions serving the universal and robust adhesive properties. These characteristics matter for ecological-evolutionary aspects and can inspire innovative designs of multifunctional, biomimetic pressure-sensitive adhesives and varnishes.
Pollinators are important drivers of angiosperm diversification at both micro- and macroevolutionary scales. Both
hummingbirds and bats pollinate the species-rich and morphologically diverse genus Vriesea across its distribution in
the Brazilian Atlantic Forest. Here, we (i) determine if floral traits predict functional groups of pollinators as documented,
confirming the pollination syndromes in Vriesea and (ii) test if genetic structure in Vriesea is driven by geography (latitudinal
and altitudinal heterogeneity) or ecology (pollination syndromes). We analysed 11 floral traits of 58 Vriesea species and
performed a literature survey of Vriesea pollination biology. The genealogy of haplotypes was inferred and phylogenetic
analyses were performed using chloroplast (rps16-trnk and matK) and nuclear (PHYC) molecular markers. Floral traits
accurately predict functional groups of pollinators in Vriesea. Genetic groupings match the different pollination syndromes.
Species with intermediate position were found between the groups, which share haplotypes and differ morphologically
from the typical hummingbird- and bat-pollinated flowers of Vriesea. The phylogeny revealed moderately to well-supported
clades which may be interpreted as species complexes. Our results suggest a role of pollinators driving ecological isolation
in Vriesea clades. Incipient speciation and incomplete lineage sorting may explain the overall low genetic divergence within
and among morphologically defined species, precluding the identification of clear species boundaries. The intermediate
species with mixed floral types likely represent a window into shifts between pollinator syndromes. This study reports the
morphological-genetic continuum that may be typical of ongoing pollinator-driven speciation in biodiversity hotspots.
Bromeliad scales have been investigated extensively due to their recognition as a key ecological and evolutionary feature of Bromeliaceae. However, much remains unknown about such trichomes and only recently mucilage exudation was described for them in a species of the subfamily Bromelioideae. The present study aimed to investigate the secretion present in inflorescences of Tillandsia cyanea Linden ex K. Koch (Tillandsioideae) to determine whether the scales of this species also produce and release secretions. Samples of young and mature portions of inflorescences were collected and prepared according to standard methods for light and electron microscopy. Anatomical and ultrastructural results indicate that the secretion is produced by the wing portion of typical peltate trichomes on the adaxial surface of bracts. The secretory activity begins in the early stages of trichome expansion and characteristically occurs in cells exhibiting a porous cuticle and dense cytoplasm with numerous mitochondria and dictyosomes. Histochemical tests confirmed mucilage secretion and revealed proteins in the exudate. These data comprise the first record of mucilage exudation by trichomes within Tillandsioideae and indicate that this capacity may be more relevant to bromeliad biology than previously considered. Functional aspects and colleter-like activity are also discussed.
Colleters are trichomes or emergencies that produce a sticky exudate consisting of a mixture of mucilage, lipids, terpenes, and phenolic compounds. Colleters occur in at least 60 families of angiosperms; however, reports of them are scarce for the Orchidaceae. Elleanthus brasiliensis is distinguished by the presence of an abundant gelatinous secretion that covers almost all of its inflorescences. We aimed to describe the histology of colleters in inflorescences of E. brasiliensis and Elleanthus crinipes, and to analyze the chemical composition of their secretion to better understand the functions of these secretory structures. Due to the low frequency of colleters and lack of visible secretion in E. crinipes, histochemical tests and chemical analyses were not performed for this species. Colleters are of a brush type and their secretion has, at the same time, hydrophilic and lipophilic components. Histochemical tests further revealed the presence of pectin, mucilage, lipids, terpenes, phenolic compounds, and proteins. The GC-MS analysis confirmed the presence of γ-sitosterol and palmitic, linoleic, and stearic acids in the secretion of E. brasiliensis. Infrared analysis indicated the possible presence of polysaccharides in the secretion. The occurrence of colleters in both species studied and in other orchids described in the literature suggests that these structures are common in the inflorescences of tropical orchids. In these environments, the hydrated polysaccharides in the secretion form a dense matrix that can act as a physical barrier, and terpenes may help to protect against herbivores and pathogenic microorganisms. This information broadens our knowledge of the morphological and chemical diversity of the secretions produced by orchid colleters.
Caryocar brasiliense is a flagship species of the Brazilian Cerrado. It produces flowers with a strong peculiar scent, which are pollinated by bats and occasionally moths with short mouthparts. However, the cues responsible for attracting these nocturnal pollinators remain unknown. We aimed to identify osmophores of C. brasiliense, describe the ultrastructure of the cells involved in the synthesis and release of floral odour, and identify the constituents of the floral bouquet. We performed field observations and histochemical and ultrastructural analyses of flowers focusing on the androecium. Gas chromatography-mass spectrometry was used to analyse the scents emitted. Filament epidermal cells were found to possess an unusual shape and be responsible for the main production and release of odour. These cells, called foraminous cells, are elongate and possess pores where their cell walls are abruptly thin. The cuticle is practically absent over the pores, which facilitates odour emission. The foraminous cells have conspicuous nuclei and organelle-rich cytoplasm where oil droplets can be seen prior to anthesis. The features of these cells remain similar during anthesis, but many vesicles fuse with the plasma membrane and the number of oil droplets in the cytosol decreases. Twenty-nine components were found in the scent, especially fatty acid derivatives and N- and S-bearing compounds. Our analyses revealed that the androecium of C. brasiliense has a particular structure that acts as an osmophore. The scent from the androecium resembles that of the entire flower, which is an unprecedented finding for a plant with single flowers as the pollination unit.
Background: Chiropterophily encompasses the floral traits by which bats are attracted as the main pollinators. Among the chiropterophilous flowering plants of the New World, Bromeliaceae is one of the most ecologically important families; however, information about the chiropterophilous interaction in this family is still scarce. Aims: We present a comprehensive review of bat pollination in bromeliads, covering floral traits, rewards offered to pollinators, floral attractants and the identity of visiting bat species. Methods: We discuss traits shared among chiropterophilous bromeliads and present general trends in an evolutionary context. We constructed a phylogenetic tree to elucidate the ancestral pollination syndromes of the 42 extant bromeliad species (ca. 1% of total) known to be bat-pollinated. Results: Most of the species within the ten genera reported belong to the Tillandsioideae subfamily, with three genera appearing to be exclusively bat-pollinated. Floral visitors include 19 bat species of 11 genera from the Phyllostomidae. Conclusions: Our analysis indicated that chiropterophilous floral features originated multiple times in bromeliad evolution, most probably from ornithophilous. The evidence for floral traits associated with bat pollination and the chiropterophilous syndrome presented by certain Bromeliaceae indicate the important role played by bats in the evolution of this plant family.
The taxonomic delimitation of Vriesea is challenging because several diagnostic traits of the genus are shared with other genera in Tillandsioideae. The genus has no unique morphological features that distinguish it from other taxa. Earlier phylogenetic studies suggested a polyphyletic status of this genus, but taxon sampling was limited, and tests of congruence for morphological characters have not yet been performed. Here we used a total evidence approach and a more comprehensive Brazilian taxon sampling to help circumscribe Vriesea s.s. (the lineage that contains the type species). We concatenated morphological and molecular datasets for the first time to reconstruct phylogenetic hypotheses. We used 99 morphological characters and ~4 kb of plastid data (psbA-trnH, trnK5′-rps16, matK, trnL-trnF) for 172 terminals, including nine genera of Tillandsioideae. We analysed datasets by parsimony analyses, with several weighting schemes considered for character-state changes (equal weights and an implied weighting scheme that we used as a sensitivity analysis). The concatenated data resulted in a well-resolved phylogenetic inference that provided strong evidence that the genus is not monophyletic as traditionally circumscribed. Given the congruence between morphological, molecular and geographical sources of data, we separated Vriesea into distinct lineages, and proposed a new circumscription that includes only species of Vriesea s.s. found in the Chacoan and Parana subregions.
This study aims to investigate colleters’ secretory function, on cellular level, in Rubiaceae species from contrasting environments looking to explore the association between secretion and environment. We collected samples from eight species of Rubiaceae growing in forest and savanna having standard-type colleters with diverse histochemistry (hydrophilic, lipophilic and mixed secretions) and processed for both conventional and cytochemical study under transmission electron microscopy (TEM). The standard colleters, although similar in morphology and anatomy, exhibited marked differences on cellular level, especially in the abundance and topology of Golgi bodies, endoplasmic reticulum and plastids when comparing forest and savanna species. These differences were clearly aligned with the chemical nature of the secretions they produce, with predominance of hydrophilic secretions in forest species and lipophilic or mixed secretions in savanna species. The combination of methods in electron microscopy revealed the sites of synthesis and intracellular compartmentation of substances, the mechanisms of their secretion from the protoplast and confirmed the involvement of the outer walls of the epithelial cells in the elimination of exudates to the gland surface. Our study suggests a potential environment-associated plasticity of the secretory cells of standard-type colleters in modulating their secretory function performance.
Floral anatomy and development of Saxofridericia aculeata Körn was studied in a comparative approach to contribute to the understanding of the family. Flowers at different developmental stages were analysed with light and scanning electron microscopy, and the nature of the exudate secreted by the floral trichomes was investigated by histochemical tests. The anatomical characteristics observed in S. aculeata flowers were compared with those from other Rapateaceae species by a cluster analysis (UPGMA). The dendrogram generated reflects the groupings that emerged in phylogenetic molecular analyses, highlighting the usefulness of floral anatomy for taxonomy and for the understanding of infrafamilial relationships. The exudate secreted by the trichomes has a polysaccharidic composition. Such trichomes (colleters) occur in the sepals, petals, filaments and around the gynoecium; they are initiated at mid-stage of floral development and are an apomorphy of the family. The flowers are pentacyclic, presenting three initially free sepals, petals, stamens and carpels that mature in a centripetal order. The connate portion of the corolla, which is also adnate to the stamens, has a late development by zonal growth. Gynoecium formation is a combination of postgenital and congenital fusion processes. Data on floral organogenesis of Rapateaceae are first reported here and support the early diverging position of the family in Poales, close to Bromeliaceae.
Nectar-feeding bats depend mainly on floral nectar to fulfil their energetic requirements. Chiropterophilous flowers generally present strong floral scents and provide conspicuous acoustic echoes to attract bats. While floral scents are assumed to attract bats over long distances, acoustic properties of flower structures may provide detailed information, thus supporting the localization of a flower at close ranges. So far, to our knowledge, there is no study trying to understand the relative importance as well as the combination of these generally coupled cues for detection (presence) and localization (exact position) of open flowers in nature. For a better comprehension of the significance of olfaction and echolocation in the foraging behaviour of nectar-feeding bats, we conducted two-choice experiments with Leptonycteris yerbabuenae. We tested the bats' behaviour in three experimental scenarios with different cues: (i) olfaction versus echolocation, (ii) echolocation versus echolocation and olfaction, and (iii) olfaction versus echolocation and olfaction. We used the floral scent of the bat-pollinated cactus Pachycereus pringlei as olfactory cue and an acrylic paraboloid as acoustic cue. Additionally, we recorded the echolocation behaviour of the bats and analysed the floral scent of P. pringlei. When decoupled cues were offered, bats displayed no preference in choice for any of the two cues. However, bats reacted first to and chose more often the coupled cues. All bats echolocated continuously and broadcast a long terminal group before a successful visit. The floral scent bouquet of P. pringlei is composed of 20 compounds, some of which (e.g. methyl benzoate) were already reported from chiropterophilous plants. Our investigation demonstrates for the first time to our knowledge, that nectar-feeding bats integrate over different sensory modes for detection and precise localization of open flowers. The combined information from olfactory and acoustic cues allows bats to forage more efficiently.
Vriesea é o segundo maior gênero de Tillandsioideae com 281 espécies,
distribuído predominantemente na América do Sul. No Brasil, as espécies ocorrem no
Cerrado, na Amazônia, na Caatinga, Pampa e principalmente na Mata Atlântica, bioma com a
maior riqueza específica do gênero. Na sistemática atual, Vriesea está
dividido em duas secções, Vriesea e Xiphion. Na secção
Xiphion enquadra-se grande parte do grupo V. platynema
com 41 espécies, ocorrendo desde a América Central até a Argentina. O grupo apresenta
acentuado polimorfismo, proporcionando a identificação errônea dos táxons. Neste estudo,
são reconhecidos três táxons para o Paraná, V. platynema var. platynema,
V. platynema var. variegata e V.
tijucana. Para cada táxon, são apresentadas descrições morfológicas,
comentários, chave de identificação, distribuição geográfica, ilustrações e o
status de conservação.
Many plants provide predatory arthropods with food or shelter. Glandular trichomes entrap insects and may provision predators with insect carrion, though it has not been clear whether this putative benefit functions with natural amounts of carrion, whether plants actively attract insect tourists, and how common this provisioning system is. We tested the hypothesis that a sticky columbine (Aquilegia eximia: Ranunculaceae) attracts passerby arthropods (a siren song leading them to their demise); that these entrapped arthropods increased predators on the plant; and that these predators reduced damage to the plant. Sticky traps baited with columbine peduncles entrapped more arthropod carrion than unbaited control traps. Predator abundance correlated positively with carrion abundance observationally, and experimental removal of carrion reduced predator numbers. Experimental removal of carrion also increased damage to reproductive structures, likely due to reductions in predator numbers. This indirect defense may be common; we compiled a list of insect-trapping sticky plants that includes over 110 genera in 49 families, suggesting a widespread convergence of this trait, even in non-carnivorous plants. The ubiquity of this trait combined with these experiments suggest that carrion entrapment should be viewed as a common and active process mediated by the plant for indirect defense.
Vriesea bituminosa Wawra (Bromeliaceae) inflorescences produce a sticky and abundant mucilage, covering their entire surface. Insects get trapped in this exudate when visiting the inflorescences and eventually die. The aim of this study was to record the diversity of insects captured in, and those tolerant to, the mucilage of V. bituminosa inflorescences and to discuss the ecological role of this natural trap. The study was conducted in the Atlantic Forest, in Rio de Janeiro State, Brazil. Insects were collected from 25 inflorescences of V. bituminosa. We obtained 268 individuals of 137 morphospecies of insects; similar to 50 % have phytophagous habits. We suggest that the exudate acts as a protective barrier against herbivory for this bromeliad species. However, some species such as the Epimorius suffusus moth (Pyralidae), Plunentis porosus (Coreidae), and two species of Diptera (Lauxaniidae and Drosophilidae) freely feed and reproduce on these inflorescences which suggests that they have suitable properties for utilization of the resources on the reproductive structures of this plant. The possible role of insects glued to inflorescences as a source of nutrients for this bromeliad is also discussed.
Premise of research. Croton glandulosus L. is a ruderal annual species of Euphorbiaceae native to the American tropics and widespread in urban and rural areas in Brazil. We investigated the structure, histochemistry, and ultrastructure of glands on the inflorescence axis of C. glandulosus to explore the relationship between their structure and function. Methodology. Reproductive apexes were prepared according to standard methods for plant anatomy, SEM., and TEM. Histochemical tests were performed using fresh material. Pivotal results. Mature glands are bowling pin shaped and are differentiated into a single-layered secretory epidermis arranged radially around a parenchymatous central axis supplied with xylem. In the neck region of the glands, the epidermal cells present structural components typical of lipophilic secretion, whereas the parenchyma cells are specialized in the production of hydrophilic compounds. The resinous secretion is released by cuticle pores occurring exclusively on the tip of the gland. Conclusions, This is the first report of the occurrence of colleters on the inflorescences of a Croton species. Our observations clearly indicate that glands on the inflorescence axis of C. glandulosus are resin-secreting colleters that may have important protective functions.
The presence of calycinal trichomes in Ipomoea has been neglected, which renders the interpretation of their functions difficult. The present work aims to characterise the structure, as well as the composition of the secretion of calycinal trichomes in Ipomoea cairica, in order to establish a relationship between their structure and function. Samples of floral buds at different developmental stages and sepals from fruits were collected and fixed for study under light as well as under scanning and transmission electron microscopy. The calyx of I. cairica is persistent and presents glandular trichomes which produce acidic polysaccharides. The trichomes are peltate and consist of a short stalk and a pluricellular secretory portion. The cells from the secretory portion contain a dense and organelle-rich cytoplasm. The fresh secretion is hyaline and fluid, but solidifies when exposed to low humidity, taking on a crystalline and fragile aspect, and they return to a gel state when in the presence of water. The calycinal trichomes in I. cairica show great structural and ultrastructural similarities to colleters and can be considered functionally analogous. The secretion, which is highly hygroscopic, spreads along the surface of the corolla and of the fruit, apparently protecting these structures against desiccation.
Brocchinia reducta is the first documented case of carnivory in the Bromeliaceae. Its erect leaves form a yellowish cylinder with a cuticular lubricant on its inner surface, impound fluid that emits a nectarlike fragrance, and bear trichomes capable of absorbing amino acids from this fluid in which numerous insects, mainly ants, drown. Trichome absorptivity and aspects of trichome structure appear unique in the primitive subfamily Pitcairnioideae. We present the first rigorous definition of carnivory in plants, and discuss its implications for the identification of cases of carnivory and protocarnivory in bromeliads. A cost/benefit model for the evolution of carnivory is developed to analyze why carnivorous plants are restricted mainly to sunny, moist, nutrient-poor sites and seasons, and why carnivory is rare in epiphytes and other bromeliads. The relative advantages of carnivory and ant-fed myrmecophily are discussed in terms of this model, and predictions made regarding the nature of the ant-plant mutu...
The distinctive foliar trichome of Bromeliaceae has promoted the evolution of an epiphytic habit in certain taxa by allowing the shoot to assume a significant role in the uptake of water and mineral nutrients. Despite the profound ecophysiological and taxonomic importance of this epidermal structure, the functions of nonabsorbent trichomes in remaining Bromeliaceae are not fully understood. The hypothesis that light reflection from these trichome layers provides photoprotection was not supported by spectroradiometry and fluorimetry in the present study; the mean reflectance of visible light from trichome layers did not exceed 6.4% on the adaxial surfaces of species representing a range of ecophysiological types nor was significant photoprotection provided by their presence. Several reports suggesting water repellency in some terrestrial Bromeliaceae were investigated. Scanning electron microscopy (SEM) and a new technique-fluorographic dimensional imaging (FDI)-were used to assess the interaction between aqueous droplets and the leaf surfaces of 86 species from 25 genera. In the majority of cases a dense layer of overlapping, stellate or peltate trichomes held water off the leaf epidermis proper. In the case of hydrophobic tank-forming tillandsioideae, a powdery epicuticular wax layer provided water repellency. The irregular architecture of these indumenta resulted in relatively little contact with water droplets. Most mesic terrestrial Pitcairnioideae examined either possessed glabrous leaf blades or hydrophobic layers of confluent trichomes on the abaxial surface. Thus, the present study indicates that an important ancestral function of the foliar trichome in Bromeliaceae was water repellency. The ecophysiological consequences of hydrophobia are discussed.
1. Introduction 2. Vegetative structure 3. Reproductive structure 4. Carbon and water balance 5. Mineral nutrition 6. Reproduction and life history with H. Luther and B. Bennett 7. Ecology 8. Relationships with fauna 9. History and evolution with G. Brown and R. Terry 10. Neoregelia subgenus Hylaeicum I. Ramirez 11. Cryptanthus I. Ramirez 12. Tillandsia and Racinaea W. Till 13. Tillandsioideae W. Till 14. Ethnobotany of Bromeliaceae B. Bennett 15. Endangered Bromeliacea, M. Dimmitt References Index.
Diverse invertebrate and vertebrate species live in association with plants of the large Neotropical family Bromeliaceae. Although previous studies have assumed that debris of associated organisms improves plant nutrition, so far little evidence supports this assumption. In this study we used isotopic ((15)N) and physiological methods to investigate if the treefrog Scinax hayii, which uses the tank epiphytic bromeliad Vriesea bituminosa as a diurnal shelter, contributes to host plant nutrition. In the field, bromeliads with frogs had higher stable N isotopic composition (delta(15)N) values than those without frogs. Similar results were obtained from a controlled greenhouse experiment. Linear mixing models showed that frog feces and dead termites used to simulate insects that eventually fall inside the bromeliad tank contributed, respectively, 27.7% (+ or - 0.07 SE) and 49.6% (+ or - 0.50 SE) of the total N of V. bituminosa. Net photosynthetic rate was higher in plants that received feces and termites than in controls; however, this effect was only detected in the rainy, but not in the dry season. These results demonstrate for the first time that vertebrates contribute to bromeliad nutrition, and that this benefit is seasonally restricted. Since amphibian-bromeliad associations occur in diverse habitats in South and Central America, this mechanism for deriving nutrients may be important in bromeliad systems throughout the Neotropics.
Se describen e ilustran dos nuevas especies de Hechtia, H. pretiosa y H. zamudioi. Ambos taxa son endémicos del centro de México, el primero de Guanajuato y el segundo de Querétaro.
Polyethylene glycol (400) with 90% glycerol (aqueous) is introduced as an efficient solvent system for lipid stains. Various lipid-soluble dyes were dissolved in this solvent system and tested for their intensity, contrast, and specificity of staining of suberin lamellae in plant tissue. The stability (i.e., lack of precipitation) of the various staining solutions in the presence of fresh tissue was also tested. When dissolved in polyethylene glycol-glycerol, Sudan red 7B (fat red) was the best nonfluorescent stain and fluorol yellow 088 (solvent green 4) was an excellent fluorochrome. These two dyes formed stable staining solutions which efficiently stained lipids in fresh sections without forming precipitates. Estimations of the solubilities of these dyes in the solvent compared with their solubilities in lipids of various chemical types indicated that they should both be effective stains for lipids in general.
Bromeliaceae is one of the most diverse families in terms of morphology, especially its floral structure and stigmatic variability. Nineteen different stigmatic types are observed in the family, the margins of which differ in shape and presence or absence of epidermal appendages. Although many studies have classified stigma types, those that report on stigmatic margins are rare. Therefore, in this work, we aimed to study in detail the morphology of stigmatic margins in Bromeliaceae, including micromorphology and histochemistry, characterizing the secretions produced. To accomplish this, we used both optical and electron microscopy. Stigmatic margins of the twenty-two species studied were described as crenate, laciniate, lobate, undulate, and entire. We also observed unicellular, bicellular and multicellular secretory trichomes, branched or unbranched, with two to five arms. Stigmatic secretions, such as mucilage, total lipids, starch, polysaccharide, alkaloid and essential oil, were found. By addressing the diversity of stigmatic margins, we have added to the systematics of Bromeliaceae, including the morphology and histochemistry of epidermal appendages.
Clusiaceae species are known globally for the economic importance of their secretory structures; however, reports of colleters in the family are scarce. In the present study, we characterised the leaf colleters in Clusia burchellii by investigating the morphology and anatomy of the glands, the histolocation of the major chemical substances present in the secretory cells and the cellular aspects associated with the synthesis and release of the secretions. Leaf samples at different developmental stages were collected and examined under light and electron microscopy. Histochemical tests were performed. Colleters of the standard type occur at the base of the petiole, are sessile or short pedunculated, and originate from protoderm and ground meristem cells. During leaf development, young, active, and whitish colleters become brownish and inactive at late developmental stages. Alkaloids and phenolic compounds were common in central axis cells. A mixture of hydrophilic and lipophilic substances histochemically detected, which can prevent water loss under hot tropical climates, were also found. Secretion accumulation was observed in the periplasmic region of the secretory cells and in the subcuticular spaces. Cuticular pores were present especially in the apical portion of the colleters. Our data revealed some cellular aspects of the secretion mechanisms in the leaf colleters of C. burchellii.
Vriesea is the second largest genus in Tillandsioideae, the most diverse subfamily of Bromeliaceae. Although recent studies focusing on Tillandsioideae have improved the systematics of Vriesea, no consensus has been reached regarding the circumscription of the genus. Here, we present a phylogenetic analysis of core Tillandsioideae using the nuclear gene phyC and plastid data obtained from genome skimming. We investigate evolutionary relationships at the intergeneric level in Vrieseeae and at the intrageneric level in Vriesea s.s. We sampled a comprehensive dataset, including 11 genera of Tillandsioideae and nearly 50% of all known Vriesea spp. Using a genome skimming approach, we obtained a 78 483-bp plastome alignment containing 35 complete and 55 partial protein-coding genes. Phylogenetic trees were reconstructed using maximum-likelihood based on three datasets: (1) the 78 483 bp plastome alignment; (2) the nuclear gene phyC and (3) a concatenated alignment of 18 subselected plastid genes + phyC. Additionally, a Bayesian inference was performed on the second and third datasets. These analyses revealed that Vriesea s.s. forms a well-supported clade encompassing most of the species of the genus. However, our results also identified several remaining issues in the systematics of Vriesea, including a few species nested in Tillandsia and Stigmatodon. Finally, we recognize some putative groups within Vriesea s.s., which we discuss in the light of their morphological and ecological characteristics.
Vriesea is the second largest genus in Tillandsioideae, the most diverse subfamily of Bromeliaceae. Although recent studies focusing on Tillandsioideae have improved the systematics of Vriesea, no consensus has been reached regarding the circumscription of the genus. Here, we present a phylogenetic analysis of core Tillandsioideae using the nuclear gene phyC and plastid data obtained from genome skimming. We investigate evolutionary relationships at the intergeneric level in Vrieseeae and at the intrageneric level in Vriesea s.s. We sampled a comprehensive dataset, including 11 genera of Tillandsioideae and nearly 50% of all known Vriesea spp. Using a genome skimming approach, we obtained a 78 483-bp plastome alignment containing 35 complete and 55 partial protein-coding genes. Phylogenetic trees were reconstructed using maximum-likelihood based on three datasets: (1) the 78 483 bp plastome alignment; (2) the nuclear gene phyC and (3) a concatenated alignment of 18 subselected plastid genes + phyC. Additionally, a Bayesian inference was performed on the second and third datasets. These analyses revealed that Vriesea s.s. forms a well-supported clade encompassing most of the species of the genus. However, our results also identified several remaining issues in the systematics of Vriesea, including a few species nested in Tillandsia and Stigmatodon. Finally, we recognize some putative groups within Vriesea s.s., which we discuss in the light of their morphological and ecological characteristics.
The peltate trichomes of Bromeliaceae comprise an important feature of this plant group. Although recognized for their capacity for water and nutrient absorption, little is known concerning their secretory functions. This study aimed to identify and describe the structures observed to secrete mucilage in the inflorescences of Aechmea blanchetiana, a species of Bromeliaceae endemic to Brazil. Samples of different portions and developmental stages of inflorescences were collected and processed for study under light and electron microscopy. Mucilage is secreted by peltate trichomes covering the inflorescence axis, which have a structure typical of bromeliad scales, although often having an irregular shield commonly exhibiting a stellate outline. Secretion is performed by cells comprising the so-called wing portion of the trichome and begins even in initial stages of inflorescence expansion. In expanded portions, secretory activity ceases and the remaining secretion appears as a thin dehydrated film covering the inflorescence surface. Ultrastructural data show the presence of well-developed Golgi apparatus and endoplasmic reticulum, confirming a secretory function related to non-cellulosic polysaccharide production. We believe that the mucilage is related to protection against desiccation, especially at early stages of expansion. Such a functional role, in association with the nature and dynamics of the secretion, suggests that these structures act as colleters. As far as we know, this is the first record for exogenous secretory activity by the typical peltate trichomes of Bromeliaceae, and the first time when colleter-like functions have been considered and discussed in this family.
1. Abrasive material in the diet of herbivorous organisms comes from a variety of sources, including crystalline silica or calcium in plant tissues, accidentally ingested soil while digging or grazing, and entrapped substrate on the surfaces of plants. A wide variety of plants entrap substrate, usually with glandular trichomes.
2. A previous study demonstrated that entrapped sand provided resistance to herbivory in the field. In this study, the following questions were addressed: how does entrapped sand on Abronia latifolia (Nyctaginaceae) leaves and stems affect preference and performance of a common herbivore, the large‐bodied caterpillar Hyles lineata (Sphingidae); does this effect differ from those experienced by an internally feeding leaf miner?
3. Using a combination of experimental and observational approaches, it was found that sand comprised ∼4–5% of ingested weight during normal feeding of H. lineata caterpillars. This entrapped sand caused extensive wear to their mandibles, they avoided sand‐covered plants when given the choice, and the sand negatively impacted performance metrics, including pupal weight, development time, and growth rate. In contrast, a leaf‐mining caterpillar did not have a preference for or against feeding on sandy plants.
4. These results are similar to studies on mandibular wear due to grasses, and herbivorous insects that feed on these two plant groups may have similar morphologies. It is hypothesised that increased wear potential may be a convergent solution to abrasive plants in both mammals (hypsodonty) and insects.
Micromorphological investigations on the terpene-producing trichomes at the active secretory stage were performed on leaves and flowers of the Mexican Salvia greggii A. Gray (Lamiaceae), cultivated in Italy. Two types of glandular trichomes are described and compared: peltate, widespread on both the vegetative and the reproductive organs, and medium-stalked capitate, typical of the calyx abaxial side. The histochemical evidences indicate an exclusive terpene production for both morphotypes. TEM survey highlighted several common ultrastructural features that validated the light microscope observations, however a great variability was detected at the plastidome level. Different plastid populations characterized each trichome type, also in relation to the different distribution pattern on the plant epidermis. In the peltates plastids invariably displayed a well-developed internal membrane system and various types of osmiophilic inclusions: on the leaf and the calyx plastoglobuli were also observed, whereas on the corolla abundant starch grains. True leucoplast are only detected in the calyx capitate trichomes.
49 compounds were detected in the essential oil (EO) obtained from the aerial parts, with terpenes representing 98.76% of the total EO, besides negligible amounts of non-terpene derivatives and apocarotenoids. Sesquiterpenes and monoterpenes occurred in similar relative abundances: 52.7% versus 46.1%, respectively. Among sesquiterpenes, γ-muurolene (11.48%) and guaiol (6.15%) dominated for hydrocarbons and oxygenated compounds, respectively. β-pinene (20.24%) prevailed among the monoterpene hydrocarbons, resulting also as the most abundant compound in the essential oil. 1,8-cineole (11.00%) is the dominant compound of the oxygenated monoterpenes.
The ultrastructural appearance of the plastidome was linked with the various terpene classes present in the EO profile. We argued that monoterpenes were probably synthetized in the calyx capitate trichomes and the sesquiterpenes in the peltates.
Premise of research. Casearia sylvestris (Salicaceae) is widely used in traditional medicine and possesses various types of secretory structures, but the mechanisms and compartments involved in the secretory processes have not been elucidated. This study aims to describe the chemical nature of the secretions produced by all secretory structures of C. sylvestris leaves and to identify the compartments and mechanisms of synthesis, storage, and release of secretion. Methodology. Shoot samples were collected and analyzed using standard techniques for light microscopy and for scanning and transmission electron microscopy. Histochemical tests were performed to identify the main classes of exudate compounds. Pivotal results. The subcellular compartments involved in the secretory process of the taniferous idioblasts, cavities, ducts, and colleters were identified, with all organelles being consistent with the chemical nature of secretion. In the colleters, plastids with osmiophilic compounds are related to the production of oil, while dictyosomes are associated with syntheses of polysaccharide secretion. The smooth endoplasmic reticulum, periplastidial reticulum, and plastids present in the secretory epithelium of the cavities and ducts produce the oleoresin, while dictyosomes are involved with hydrophilic secretion.
Conclusions. Ultrastructure variation among the organelles of the four types of secretory structures studied, as well as the chemical complexity of exudates produced by them, revealed particularities that enabled the description of models for the secretory mechanism of each. Novelties that reveal the mechanisms involved in the release of secretion through the cell wall are presented.
Young fronds from several fern species are covered by mucilage, but its synthesis and functional roles remain understudied. The young leaves of the tropical ferns Amauropelta cheilanthoides, Amauropelta pachyrhachis and Steiropteris decussata are covered by a hyaline layer of highly hydrophilic mucilage that is produced by glandular trichomes (GTs). In order to better understand the morphology and ultrastructure associated with mucilage secretion in these plants, we employed a combination of light and electron microscopy along with histochemical studies. The distribution and abundance of GTs varies during leaf growth. The origin and differentiation of GTs occurs early in leaf development and their secretory activity is restricted to the first stage of leaf differentiation. Glandular trichomes can be sessile or pedunculate and the secretory head commonly shows a single cell in the distal portion. In general, at the beginning of development, the distal secretory cell has a large nucleus, thin wall and dense cytoplasm with large vacuoles, endoplasmatic reticulum and active dictyosomes. In mature secretory cells the large vacuole is filled with secretion, and represents almost the entire protoplast. Observations of the early onset and duration of functional mucilaginous trichomes of Thelypteridaceae, the physicochemical nature of the secretion and the location of these trichomes indicate that the product of these structures provides protection for the apical meristem and young leaves from excessive sunlight and high levels of transpiration, thereby reducing water loss. This functional concept is the common link connecting most reports on the structure of colleters and, therefore, this work represents the first report of colleters for ferns.
This article surveys the structural, functional and phylogenetic significance of colleters in different dicotyledonous families. Colleters are multicellular secretory structures attached to the stipule, petiole, lamina, bract, bracteole, calyx and corolla. Colleters are grouped into standard (S), dendroid (D) and brush-like (B) types on the basis of their morphology and structure. D and B-type colleters occur in certain members of Rubiaceae that also have bacterial leaf nodules. Besides the normal structure, epithelial hairs, thin-walled subepidermal cells, laticifers and vasculature are present in many colleters of Apocynaceae. It is probable that the colleter functions to protect the developing meristem by secreting a viscous fluid. Exudate of D-type colleters are mucilaginous, providing the substrate necessary for the nutrition of endophytic bacteria.
Abstract— Vriesea is a large genus comprising several groups of species with controversial limits. The taxonomic revision of small monophyletic groups has been an important approach to improve our understanding of the taxonomy of the genus. After the taxonomic revision of the monophyletic group belonging to Vriesea sect. Xiphion, comprised of species with simple inflorescences, flowers patent during anthesis and not secund, and decurrent floral bract bases, this paper describes three species as new: Vriesea carmenae , Vriesea gelatinosa , and Vriesea zildae ; and proposes one synonym. The species occur mainly in the Brazilian Atlantic Forest and Cerrado domains, and are morphologically similar to V. bituminosa and V. wawranea.
The ultrastructure of the whole cellular system which forms the absorbing trichome of Tillandsia usneoides L. was studied under conditions of water stress and moisture. Cytological modification which are associated with so special a modality of functioning, were identified. The trichome is tipically divided into two parts: the «shield» whose cells form a central disk and a wing; the «stalk» whose structure includes a dome cell, two intermediate cells and two foot cells. All the walls of the absorbing system cells did not show any differences under the two physiological conditions assayed. No differences were observed also between the cytoplasm of the «shield» cells in the two experimental conditions. However, the cytoplasm of the central disk cells remained vital implying that they play an active role under both conditions, in this portion of the trichome, as regards the choise of nutrient solutions. The most important ultrastructural aspects were offered by the cytoplasm of «stalk» cells under both conditions. During the water stress phase, the cytoplasm of both the dome cell and the intermediate cells presented large central nuclei as well plastids with in a rarefied cytoplasmic matrix; very developed endoplasmic reticulum which was primarily rough; active dictyosomes and lipidie vacuolized drops. Only in the moisture phase did the cytoplasm of the dome cell form a large chamber between the wall and plasmalemma. This chamber was full of material which was P.A.S. positive. The plasmalemma appeared characteristically infolded; numerous microtubules and mitochondria were visible near it. The cytoplasmic matrix of the intermediate cells was dense; the smooth endoplasmic reticulum was very dilated. During this phase, a large increase in the vacuome of the foot cells was noted. All these ultrastructural features seem to support the idea that Tillandsia trichome is a glandular structure. From this point of view, the passage of nutrients across the complex cellular system is favoured by the presence of water avid material which originated during a cytoplasmic secretion process.
The occurrence of colleters in Eudicotyledons is probably significantly underestimated as a consequence of the scarcity of structural studies directed towards them and the difficulties to determine their function. The present work aims to report the occurrence of colleters in Cariniana estrellensis and describe their morphological and functional aspects; for this, leaves at different stages of expansion were collected and studied using light, and scanning and transmission electron microscopy. The young leaves of C. estrellensis are involute and have colleters along the margins. These colleters appear to be functional in very young leaves and produce pectic secretions that spread over the entire leaf surface. The colleters are clavate and sessile, and have a central axis composed of parenchymatic cells as well as a secretory epidermis covered by a cuticle. The central cells have vacuolate cytoplasm with few organelles and reserve substances. The cytoplasm of the epidermal cells has numerous dictyosomes during the secretory phase, with few plastids and mitochondria. The secretions coating on the leaf surfaces appear to contribute to maintaining the water balance of the young leaves, thus the main function of the colleters in this species appears to be to protect the leaves from excessive transpiration loses.
Colleters are widely occurring in eudicots showing relevant taxonomic importance in several families. Nevertheless, there are few records in monocots, restricted to only one description of these glands in Orchidaceae. The genus Oncidium is polyphyletic, currently the subject of taxonomic studies. In this context, the secretory structures can be an important diagnostic character that may help in the delineation of this group. O. flexuosum Sims presents colleters in vegetative – leaf primordium of protocorms, apical and axillary buds in the mature rhizomes – and reproductive organs – at the base of bracts, bracteoles and sepals. All the colleters observed are finger-like trichomes, composed of two uniseriated cells, where the apical one is elongated and possesses dense cytoplasm. The exsudate accumulates in a subcuticular space, causing displacement of the cuticle. Histochemical tests indicate the presence of mucilage in association with lipophilic and proteinic compounds inside the secretory cell. Secretion is abundant, hyaline and slightly viscous. The localization of the trichomes and their exsudate indicate the involvement of these colleters with the protection of meristematic regions in vegetative and reproductive organs. These results can be useful in the taxonomy of the genus Oncidium and for future studies about colleters in monocots.
The unbranched nonarticulated laticifer, including its latex, and capitate glandular trichomes from Cannabis sativa L. were analyzed in fresh and cryostat preparations with histochemical procedures for the presence of cannabinoids, alkaloids, and other selected cellular components. A positive response to cannabinoid indicators, Duquenois-Negm, fast blue salt B, Gibb, and Beam reagents occurred in laticifers, as well as exuded latex and in disc cells of epidermal capitate glandular trichomes. No response or only an apparent background response to these reagents was detected in other cells. Alkaloids were detected histochemically in laticifers and exuded latex with Wagner, Dittmar, Ellram, chromic acid, Hager, and Dragendorff reagents. Alkaloid indicators also reacted with capitate glandular trichomes but did not show a positive response in other cells of the plant. Laticifers also contained other specialized contents including the enzymes, cytochrome oxidase, and lipase. Free lipids and storage proteins were not detected in laticifers. Qualitative responses to these histochemical procedures were similar in laticifers and capitate glandular trichomes from various regions and organs of the plant axis. Histochemical indicators can be useful for preliminary surveying of specialized cell types and tissues for the presence of specialized substances.
1.
The polychromatic staining of plant cell walls by toluidine blue O is described and illustrated.
2.
The effects of various common fixatives and the effects of the pH of the staining solution are evaluated.
3.
Simple and rapid procedures are described for preparing stained temporary mounts of fresh material, or permanent mounts of embedded and sectioned material.
4.
The relationship between the polychromatic staining observed and the lignification of the walls is discussed.
An ultrastructural study of dry and wet trichomes from the upper leaf surface of pineapple revealed that shield cells were normally dead and stalk cells were often living. In stalk cells of dry trichomes, polysaccharide material was present within vacuoles and a layered material was present between the plasma membrane and cell wall. In stalk cells of trichomes wet for 12 h vacuoles were enlarged and appeared to contain little material. Layered material between the plasma membrane and cell wall was also absent. In both wet and dry trichomes, numerous mitochondria were present and plasmodesmata were observed connecting stalk, foot, and adjacent epidermal and mesophyll cells. It is suggested that the large numbers of mitochondria, which indicate high metabolism, and the numerous plasmodesmata connecting the cells, provide indirect evidence for the function of the trichomes in uptake of dissolved nutrients.