Epiphytic plants and desert plants) have absorptive hairs or scales on the leaf epidermis through which rain and dew can be absorbed.
Peronospora, or to the young mycelia of epiphytic parasites, e.g.
As in the IndoMalayan sub-region, epiphytic orchids are probably most numerous in point of species, but the genera and even sub-tribes are far more restricted in their range than in the Old World; 4 sub-tribes with 74 genera of Vandeae are confined to South America, though varying in range of climate and altitude.
The country is exceedingly rich in Aroids, many of which are epiphytic, festooning the trunks of tall trees with a magnificent drapery of abundant foliage.
Ground orchids and tree orchids are well represented; Polystachya liberica, an epiphytic orchid with sprays of exquisite small flowers of purple and gold, might well be introduced into horticulture for its beauty.
Probably many of the ferns were epiphytic. Pecopteris, Cyclopteris, Neuropteris, Alethopteris, Sphenopteris are common genera; Megaphyton and Caulopteris were tree ferns.
Such obligate parasites may be epiphytic (Erysipheae), the mycelium remaining on the outside and at most merely sending haustoria into the epidermal cells, or endophytic (Uredineae, Ustilagineae, &c.), when the mycelium is entirely inside the organs of the host.
An epiphytic fungus is not necessarily a parasite, however, as many saprophytes (moulds, &c.) germinate and develop a loose mycelium on living leaves, but only enter and destroy the tissues after the leaf has fallen; in some cases, however, these saprophytic epiphytes can do harm by intercepting light and air from the leaf (Fumago, &c.), and such cases make it difficult to draw the line between saprophytism and parasitism.
Euphaeophyceae are almost exclusively marine, growing on rocks and stones on the coast, or epiphytic upon other algae.
In epiphytic forms the rhizoids of the epiphyte often penetrate into the tissue of the host, and certain epiphytes are not known to occur excepting in connexion with a certain host; but to what extent, if any, there is a partial parasitism in these cases has not been ascertained.
Many are epiphytic on other algae, more especially the larger Phaeophyceae and Rhodophyceae.
As in the case of epiphytic brown seaweeds, the rhizoids of the epiphyte often penetrate the substance of the supporting alga.
Even among Bangiaceae the carpospores arise from the fertilized cell by division, while in all other Rhodophyceae the oospore, as it may be called, gives rise to a filamentous structure, varying greatly in its dimensions, epiphytic, and to a large extent parasitic upon the egg-bearing parent plant, and in the end giving rise to carpospores in the terminal cells of certain branches.
There is here obviously a certain parallelism with the case of Bryophyta, where the sporogonium arising from the oospore is epiphytic and partially parasitic upon the female plant, and always culminates in the production of spores.
- Stems tuberous or columnar, not infrequently branched, rarely epiphytic (Peruvian species of Zamia); fronds pinnate, bi-pinnate in the Australian genus Bowenia.
A number of species of Lycopodium are epiphytic and those of Isoetes live submerged in water.
Psilotum lives epiphytically or in soil rich in humus, while Tmesipteris is epiphytic (and, it has been suggested, partially parasitic) upon stems of tree ferns: the former has small scale-like leaves; those of the latter are of considerable size.
The Ferns exhibit a wide range in size from the minute epiphytic Hymenophyllaceae, with leaves barely a centimetre in length, to gigantic tree-ferns 80 ft.
Thus there are a few 3 Ferns which climb, others are .8 water plants, while many, especially those which live as epiphytes, are more or less xerophytic. Some of the epiphytic forms (Polypodium quercifolium, Platycerium) have strongly dimorphic leaves, the sterile leaves serving in some cases to catch falling debris, and thus to provide the plant with soil.
Many of the species inhabit situations in which the air is constantly moist, especially in the tropics; some are terrestrial; others, some of which are very minute, are epiphytic on tree-stems. A single solid central cylinder is found in the rhizome.