256 TROPICAL NATURE II 
of palms or of tree-ferns. Some grow best over water, others 
must be elevated on lofty trees and well exposed to sun and 
air. The wonderful variety in the form, structure, and colour 
of the flowers of orchids is well known; but even our finest 
collections give an inadequate idea of the numbers of these 
plants that exist in the tropics, because a large proportion of 
them have quite inconspicuous flowers and are not worth 
cultivation. More than thirty years ago the number of known 
orchids was estimated by Dr. Lindley at three thousand species, 
in Bentham and Hooker’s Genera Plantarum at five thousand, 
and it is not improbable that they may be now nearly six 
thousand. But whatever may be the numbers of the collected 
and described orchids, those that still remain to be discovered 
must be enormous. Unlike ferns, the species have a very 
limited range, and it would require the systematic work of a 
good botanical collector during several years to exhaust any 
productive district—say such an island as Java—of its orchids. 
It is not therefore at all improbable that this remarkable 
group may ultimately prove to be the most numerous in 
species of all the families of flowering plants. 
Although there is a peculiarity of habit that enables one 
soon to detect an orchidaceous plant even when not in flower, 
yet they vary greatly in size and aspect. Some of the small 
creeping species are hardly larger than mosses, while the larger 
Grammatophyllums of Borneo, which grow in the forks of trees, 
form a mass of leafy stems ten feet long, and some of the 
terrestrial species—as the American Sobralias—grow erect to 
an equal height. The fleshy aerial roots of most species give | 
them a very peculiar aspect, as they often grow to a great 
length in the open air, spread over the surface of rocks, or 
attach themselves loosely to the bark of trees, extracting 
nourishment from the rain and from the aqueous vapour of 
the atmosphere. Yet notwithstanding the abundance and 
variety of orchids in the equatorial forests, they seldom 
produce much effect by their flowers. This is due partly to 
the very large proportion of the species having quite incon- 
spicuous flowers ; and partly to the fact that the flowering 
season for each kind lasts but a few weeks, while different 
species flower almost every month in the year. It is also 
due to the manner of growth of orchids, generally in single 
