574 A TEXTBOOK OF BOTANY [Cn. XIV 



the plants, from which they cannot be wholly excluded. 

 Correspondingly the plants which grow in such places exhibit 

 xerophytic adaptations against large loss of water and hence 

 much absorption. While many of the plants of bogs, heaths, 

 and moors are xerophytic forms of ordinary shrubs and 

 herbs, two distinctive oxalophytic vegetation forms occur. 



HEATH SHRUBS ; low, dense-growing, more or less ever- 

 green, well protected against transpiration, as illustrated 

 in Rhodora, Ledum, Cassandra, Kalmia, and others of that 

 ilk, which grow not only on bogs, but along the shores of 

 deadwater streams. HEATHER SHRUBS; low or creeping, 

 evergreen with scale leaves, typified by Heather, Crowberry, 

 and others of dry, barren, exposed moors, where often the 

 peaty soil is but a few inches deep. Allied is the form of the 

 Blueberry, Huckleberry, etc. 



Other inorganic habitats are recognized in exact studies, 

 though for the most part they possess no distinctive vegeta- 

 tion forms. Thus, sand dunes and beaches, dry habitats, bear 

 a vegetation of xerophytic grasses, herbs, shrubs, and trees, 

 but no peculiar forms. Exposed rocks and cliffs, subject 

 to desiccation, have likewise no peculiar forms, unless the 

 rosette perennials, or the Lichens, should here be placed. 

 Finally, arctic and alpine tracts beyond the tree line, char- 

 acterized by coldness, have meadows of moss-like herbs, 

 trees which are condensed towards the ground, shrubs 

 which are creeping, and one characteristic vegetation form. 

 TUSSOCK PLANTS, dense, radiating, perennial, hemispherical 

 heads resting on the ground, either Mosses, Grasses, or other 

 flowering plants ; typified by some Pinks (Fig. 390) and es- 

 pecially by the remarkable Vegetable Sheep (Raoullia) of 

 New Zealand. 



3. THE ORGANIC HABITATS, AND THE VEGETATION FORMS 

 WHICH INCLUDE HYSTEROPHYTES. 



Here we may include all habitats created by the existence 

 of organisms, whether serving as a source of food, or simply 



