44 



GEOGRAPHICAL DISTRIBUTION OF PLANTS. 



which, in artificial culture, require the rock or stones for some species to be 

 kept dry, and in others to be kept moist by artificial springs of water. 



(9.) Sandy soils, in inland situations, dry or moist, which are easily imi- 

 tated, and in which a greater or less number of plants will grow according 

 to the supply of water. Bulbous plants are particularly^ adapted for such 

 soils, because they are driest in summer when the bulb is at rest. When 

 dry, sandy soils are warmer than any others. 



(10.) Forests, copses, and hedges, the plants of which include trees and 

 shrubs, deciduous or evergreen, and the plants which grow in their shade. 

 Among these are some few which grow under the constant shade of ever- 

 green trees, as the Pyrola in pine-groves ; and others which require light in 

 winter and spring, and are found growing only under deciduous trees, as the 

 common /S'cilla nutans and many bulbs, the Cowslip, and various other 

 plants found under the shelter of hedges. Climbmg and twining plants 

 are commonly found in stations of this description. 



(11.) Mountainous or Alpine regions, the plants of which include such as 

 grow on mountains of moderate height, which are clothed with vegetation to 

 their summits, and are consequently subject to greater drought in summer 

 than in winter ; and those which grow on mountains, the summits of which 

 are covered with perpetual snow, which, from its melting partially in summer, 

 keeps the surface- soil of the mountain moister at that season than during 

 winter. It is evident, however, that much must depend on the soil of the 

 mountain ; for a peaty or clayey soil will be kept in a state of greater mois- 

 ture than one which is composed chiefly of sand, and a deep soil will 

 retain more moisture than a thin stratum on rock. In the culture of moun- 

 tain plants, therefore, the particular kind of soil in which they are found 

 naturally, and its condition with regard to moisture, are of much greater 

 importance than its elevation. In short, it is found that the mountain 

 plants of the Highlands of Scotland may, with scarcely any exceptions, be 

 cultivated with success in the botanic gardens of Edinburgh and Glasgow, 

 which are on a level with the sea. 



(12.) Subterranean stations are either dark caverns where some species of 

 acrogens are found, or, as in the case of the Truffle, the interior of the soil 

 itself. The culture of the Truffle is still a desideratum in horticulture. 



(13.) Living or dead t7-ees or other plants constitute a station. Parasitic 

 plants, such as the Mistletoe and the Dodder, root into the stems of living 

 trees, and their dissemination can be effected by art as well as by nature. 

 Epiphytes or pseudo-parasites grow either upon dead or living vegetables, 

 but without deriving any nourishment from their vital parts. Of these, 

 we have in Britain the common Polypod}^, a fern found on the rough bark 

 of old trees, especially Oaks, in moist climates, as about the lakes of Cumber- 

 land and ^Westmoreland ; and on old pollards in many situations. There 

 are also numerous Mosses, Lichens, and Fungi, which live on the outer bark 

 of old trees in temperate regions ; and an immense number of Orchidaceae 

 which have their stations on trees in tropical climates, and the culture of 

 which in British stoves has recently called forth an extraordinary degree of 

 ingenuity among gardeners. 



] 49. To these stations botanists have added some others ; such as the rub- 

 bish near human dwellings, which is supposed to have an attraction for certain 

 plants from containing nitrogen ; roadsides, &c. : but, with a view to culture, 

 these, and several which have been mentioned, are of no great importance. 



