SUMMARY
Secretory tissues occur in most vascular plants. Some of these tissues, such as hydathodes, salt glands and nectaries, secrete unmodified or only slightly modified substances supplied directly or indirectly by the vascular tissues. Other tissues secreting, for instance, polysaccharides, proteins and lipophilic material, produce these substances in their cells. The cells of secretory tissues usually contain numerous mitochondria. The frequency of other cell organelles varies according to the material secreted. In most glandular trichomes the side wall of the lowest stalk cell is completely cutinized. This prevents the secreted material from flowing back into the plant.

The salt glands in Atriplex eliminate salt into the central vacuole of the bladder cell but, in other plants, the glands secrete salt to the outside. Different views exist as to the manner in which salt is eliminated from the cytoplasm. According to some authors, the mode of elimination is an eccrine one, while others suggest the involvement of membrane-bound vesicles.

Nectar is of phloem origin. The pre-nectar moves to the secretory cells through numerous plasmodesmata present in the nectariferous tissue. Nectar is eliminated from the secretory cells by vesicles of either KR or dictyosomal origin. In some cases, both organelles may be involved but an eccrine mode of nectar secretion has also been suggested by some authors.

Carbohydrate mucilages and gums are synthesized by dictyosomes but virtually every cell compartment has been suggested as having a role on the secretion of lipophilic substances. Most commonly, plastids are implicated in the synthesis of lipophilic materials but KR may also play a part. In some cases lipophilic materials may be transported towards the plasmalemma in the KR.

Resin and gum ducts of some plants develop normally or in response to external stimuli, such as microorganisms or growth substances. Among the latter, ethylene is the most effective.

During the course of evolution, secretory tissues seem to have developed from secretory idioblasts scattered among the cells of the ordinary tissues. Subsequently ducts and cavities developed and finally secretory trichomes.

Secretory tissues in vascular plants

Cladistic parsimony analyses of rbcL nucleotide sequence data from 171 taxa representing nearly all tribes and subtribes of Orchidaceae are presented here. These analyses divide the family into five primary monophyletic clades: apostasioid, cypripedioid, vanilloid, orchidoid, and epidendroid orchids, arranged in that order. These clades, with the exception of the vanilloids, essentially correspond to currently recognized subfamilies. A distinct subfamily, based upon tribe Vanilleae, is supported for Vanilla and its allies. The general tree topology is, for the most part, congruent with previously published hypotheses of intrafamilial relationships; however, there is no evidence supporting the previously recognized subfamilies Spiranthoideae, Neottioideae, or Vandoideae. Subfamily Spiranthoideae is embedded within a single clade containing members of Orchidoideae and sister to tribe Diurideae. Genera representing tribe Tropideae are placed within the epidendroid clade. Most traditional subtribal units are supported within each clade, but few tribes, as currently circumscribed, are monophyletic. Although powerful in assessing monophyly of clades within the family, in this case rbcL fails to provide strong support for the interrelationships of the subfamilies (i.e., along the spine of the tree). The cladograms presented here should serve as a standard to which future morphological and molecular studies can be compared.

A phylogenetic analysis of the Orchidaceae: evidence from rbcL nucleotide sequences

Structure and function of secretory cells.

Many plants take up soluble monosilicic acid from the soil. Some of these plants subsequently deposit it as cell inclusions of characteristic structure. This article describes the distribution and diversity of opaline silica bodies in monocotyledons in a phylogenetic framework, together with a review of techniques used for their examination, and the ecology, function and economic applications of these cell inclusions. There are several different morphological forms of silica in monocot tissues, and the number of silica bodies per cell may also vary. The most common type is the “druse-like” spherical body, of which there is normally a single body per cell, more in some cases. Other forms include the conical type and an amorphous, fragmentary type (silica sand). Silica bodies are most commonly found either in the epidermis (e.g., in grasses, commelinas and sedges) or in the sheath cells of vascular bundles (e.g., in palms, bananas and orchids). Silica-bearing cells are most commonly associated either with subepidermal sclerenchyma or bundle-sheath sclerenchyma. Silica bodies are found only in orchids and commelinids, not in other lilioid or basal monocots. In orchids, silica bodies are entirely absent from subfamilies Vanilloideae and Orchidoideae and most Epidendroideae but present in some Cypripedioideae and in the putatively basal orchid subfamily Apostasioideae. Among commelinid monocots, silica bodies are present in all palms, Dasypogonaceae and Zingiberales but present or absent in different taxa of Poales and Commelinales, with at least four separate losses of silica bodies in Poales.

Systematics and Biology of Silica Bodies in Monocotyledons

Calcium Oxalate Crystals in Monocotyledons: A Review of their Structure and Systematics

Ultrastructure of osmophores in Restrepia (Orchidaceae)

Species of the Neotropical orchid genus Stanhopea produce a fragrance comprising terpenoids and aromatics which attracts euglossine bee pollinators The secretory tissue, called an osmophore, is located in the adaxial region of a sac formed near the proximal portion of the floral lip This region is easily recognized in Stanhopea oculata and S wardii because it is papillate The osmophore in these two species includes all the cells of the papillae and those directly below, that grade into fundamental tissue Osmophore cells are more densely cytoplasmic than cells in the adjacent tissue Numerous amyloplasts and mitochondria are seen in these cells from the earliest bud stages we examined through anthesis Smooth and rough endoplasmic reticulum are abundant, but dictyosomes are uncommon Mitochondria of osmophore cells appear to be distributed with no apparent pattern during bud stages, although they tend to be aligned near the plasmalemma at anthesis Osmophore cells are highly vacuolate after anthesis STANHOPEA Frost ex Hooker is a Neotropical genus of Orchidaceae consisting of about 50 species Members of Stanhopea are epiphytic herbs with ovoid or subcylindric, ribbed, unifoliate pseudobulbs (Fig la) Leaves are plicate, elliptic to narrowly elliptic, cQnspicuously nerved, and distinctly petiolate Inflorescences are sharply pendent from the base of the pseudobulb (Fig 1-3) and bear 2-15 large, showy, short-lived, intensely aromatic flowers (Fig 1, 4) The median sepal is coriaceous, erect, and free; lateral sepals are connate at their lower margins and adnate to the lip Petals are narrower and less coriaceous than the sepals, and usually are reflexed strongly between them The lip (Fig lb, 4, 5) is thick, fleshy, glossy, and usually divided into a basal, saccate hypochile, a mesochile bearing conspicuous horns, and a flattened, distal epichile The fragrance emitting portion of the flower, or osmophore, of S oculata and S wardii consists of a papillate layer of tissue situated in the pouch of the hypochile (Fig lb, 5, 6) The column is elongate, usually broadly winged, and arched toward the lip The anther is terminal with two pollinia I Received for publication 1 April 1986; revision accepted 29 December 1986 We acknowledge Terry W Lucansky, University of Florida, and Norris H Williams, Florida State Museum, for critical reading of the manuscript and helpful suggestions for improvement; Ann L Curry, University of Florida, for her generous technical assistance; and Alan A Atchley, USDA, Beltsville, Maryland, for supplying classical literature This study was supported in part by a grant from the National Science Foundation, DEB 82-19120 We recognize substantial assistance from the Florida Agricultural Experiment Station of which this paper is number 7209 in the Journal Series Stanhopea is one of several Neotropical orchid genera pollinated by euglossine bees There are published reports of the biology of these plants and their pollinating bees, of the chemistry of the compounds (mostly terpenoids and aromatics; Williams and Whitten, 1983) comprising the fragrances emitted by the flowers, and of the interactions between bee and flower Dodson et al (1969) and Dressler (1968, 1982) have studied the euglossine-bee-pollination syndrome in orchids They reported that only male bees are associated with pollination, and that bees are attracted to the flowers by the strong fragrances they collect, presumably as a percursor for a sex pheromone they synthesize Osmophore structure has been studied in orchids with light microscopy by Vogel (1 96 3), with scanning electron microscopy by Williams (1983), and with both scanning and transmission electron microscopy by Pridgeon and Stern (1983, 1985) The term osmophore (osmoforo from Gr osmo, odor, and pherein, to bear) was first used by G Arcangeli (1883) who applied it to the fragrant spadix of certain members of the Araceae (eg, Dracunculus vulgaris, Amorphophallus rivieri) The external morphology of the osmophores in Stanhopea and other euglossine-bee-pollinated taxa varies from the numerous mounds of tissue in Clowesia and the trichomes of Polycycnis to the papillae in some species of Stanhopea and smooth tissue of other species Williams ( 19 8 3) noted that in this group of orchids "the structure of the osmophore region is quite variable from species to species, and from genus to genus"

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Osmophores of stanhopea (orchidaceae)

Icones Pleurothallidinarum XX. Systematics of Jostia, Andinia, Barbosella, Barbrodria, Pleurothallis Subgen Antilla, Subgen Effusia, subg. Restrepiodia. Addenda to Lepanthes, Masdevallia, Platystele, Pleurothallis, Restrepiopsis, Scaphosepalum and Teagueia. Monogr. Syst. Bot. Missouri Bot. Gard. 79

Tilosomes, also called "fibrous bodies" or "rod bodies" in older literature, are lignified excrescences from the walls of cells of the innermost velamen cell layer adjacent to thin-walled passage cells of the exodermis in roots of many epiphytic orchids. Seven broad morphological types are recognized: spongy, lamellate, discoid, webbed, meshed, baculate, and plaited. Some types characterize specific genera or subtribes of Orchidaceae. Of the 350 species in 175 genera included in a survey of the family, tilosomes occur in 95 species and 39 genera and are concentrated in tribe Polystachyeae and subtribes Sobraliinae, Coelogyninae, Laeliinae, Pleurothallidinae, Bulbophyllinae, Lycastinae, and Maxillariinae. With the exception of the pantropical genera Bulbophyllum and Polystachya and the Paleotropical subtribe Coelogyninae, tilosomes are almost exclusively Neotropical phenomena.

Alec M. Pridgeon

Papers

Ultrastructure of osmophores in Restrepia (Orchidaceae)

Osmophores of stanhopea (orchidaceae)

Icones Pleurothallidinarum XX. Systematics of Jostia, Andinia, Barbosella, Barbrodria, Pleurothallis Subgen Antilla, Subgen Effusia, subg. Restrepiodia. Addenda to Lepanthes, Masdevallia, Platystele, Pleurothallis, Restrepiopsis, Scaphosepalum and Teagueia. Monogr. Syst. Bot. Missouri Bot. Gard. 79

Tilosomes in roots of orchidaceae morphology and systematic occurrence

Comparative vegetative anatomy and systematics of Spiranthoideae (Orchidaceae)