HOLE : SOME INDIAN GRASSES AND THEIR CECOLOGY. 9 



they can never be exposed to the danger of prolonged drought. Adapted to such conditions 

 are plants that show a relatively weak development of the above-mentioned arrangements 

 for regulating transpiration : in this respect these plants stand midway between hydro- 

 phytes and xerophytes. The leaves are large, and far more varied in form than in xero- 

 phytes; teeth and other incisions of the margin are common, as are compound or richly 

 divided leaves ; hydathodes seem to be frequent ; the vegetative organs are of a fresh green, 

 and devoid of thick grey coatings of hair or bluish incrustations of wax; the leaves are 

 usually dorsiventral in structure. Stomata are numerous, often occurring also on the 

 upper face of the leaf; anatomical peculiarities, such as aqueous tissues, are very rare, or 

 at least not extremely developed." 1 



Among the most typical forest trees of this group is the European Beech and the 

 Indian tree which is probably most nearly allied oecologically is the Sal. 



The anatomical and morphological characters of typical xerophytes may be described 

 by the adjective xerophytic and the same term may be used for a locality where xerophytes 

 grow, or for a plant group consisting of xerophytes. 



The adjective xerophilous{ = living in, or suited to, a dry habitat) derived from the 

 corresponding substantive xerophile, is also frequently used. Similarly we have the terms 

 hydrophilous and hydrophytic, mesophilous and mesophytic. 



8. The most important natural plant group, The Forma- 

 or aggregate of individuals, at present recognised in cecological botany is the formation tion ' 

 which may be considered as corresponding to the genus of systematic botany. Warming 

 defines the formation " as a community of species, all belonging to definite growth-forms, 2 

 which have become associated together by definite external (edaphic or climatic) characters 

 of the habitat to which they are adapted. Consequently, so long as the external conditions 

 remain the same, or nearly so, a formation appears with a certain determined uniformity 

 and physiognomy, even in different parts of the world, and even when the constituent 

 species are very different and possibly belong to different genera or families. 



Therefore — 



A formation is an expression of certain defined conditions of life, and is not con- 

 cerned with floristic differences" 3 The principal formations recognised by Warming are 

 the following which he classifies as shown : — 



Hydrophilous. — Formations in marsh and water (Hydrophytes and Helophytes). 

 Xerophilous. — Formations on sour (acid), cold and saline soil, formations on rock, 

 sand, gravel and waste land, bush or scrub formations and formations on 

 desert, steppe and savannah. 



2 A growth-form is a plant characterised by its habit (e.g. tree, shrub, herb, gregarious and sporadic plants, etc.), its period of 

 vegetative activity, of flowering and fruiting, the duration of its life cycle, by the form and nature of its flowers, fruits, stems, leaves and 

 roots, in so far as such differences can be ascribed to the influence of the conditions of the plant's environment. 



s I.e., p. 140. 



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