137 

 CHAPTER XXXV 



PHYSIOGNOMY OF VEGETATION. FORMATIONS 

 ASSOCIATIONS. VARIETIES OF ASSOCIATIONS 



THE large oecological classes indicated in the preceding chapter 

 may be subdivided into various less comprehensive types of communities. 

 Popular distinctions have for a long time been drawn among divers 

 types of vegetation, to which have been allotted certain names (forest, 

 bush, meadow, moor, heath, steppe, savannah, maqui, and so forth) that 

 have been adopted as scientific terms. The leading features upon which 

 the pertinent distinctions depend are physiognomic, and thus dependent 

 upon biological relationships. For the physiognomy of vegetation is not 

 only of aesthetic, but also of scientific significance : vegetation often 

 essentially determines the physiognomy of landscape, and in this respect 

 plays a part very different from that played by animals. 1 Physiognomy 

 must therefore be scientifically considered. 



A. PHYSIOGNOMY OF VEGETATION 



The chief circumstances that determine the physiognomy of vegeta- 

 tion are : 



1. Dominant growth-forms : trees, shrubs, and herbs, of varied 

 appearance, size and shape of foliage ; mosses, lichens, and other types. 2 

 Thus arise the oecological types : forest, bush, heath, meadow, steppe, 

 and other kinds of herbaceous vegetation, moss-tundra, lichen-tundra, and 

 so forth, modifications being introduced by lianes and epiphytes. 



2. Density of vegetation (number of individuals). This de- 

 pends upon the struggles of plants with inanimate Nature, and upon 

 the biological peculiarities of growth-forms. In some communities 

 the soil is densely covered, as in the case of meadow, but in others the 

 vegetable covering is so open that the colour of the soil imparts to the 

 landscape its hue. A distinction must therefore be drawn between 



(a) open formations evoked by shifting soil (seashore, dunes), extreme 

 character of soil (rock), dryness of climate (in desert and steppe), or by 

 extreme cold (in Polar countries), and 



(b) closed formations composed of species that grow in company 3 for 

 some reason or other, whether it be that, like some species of trees, they 

 can suppress all competition by their shade, or, like Phragmites, can 

 form dense associations by means of richly branched horizontal rhizomes. 

 A number of different species can together form one closed formation. 4 



3. Height of vegetation. Comparisons may be instituted between 

 forest, bush, and heath, all composed of woody plants, or between the 

 tall grass of a lowland meadow and the low sward of an alpine one, 

 or between forest and tundra. Many formations exhibit strata or storeys 

 of growth-forms : the greatest number of storeys will probably be found 

 in well-lighted, therefore thinly wooded, forest. 



1 Darwin writes : ' A traveller should be a botanist, for in all views plants 

 form the chief embellishment.' 



2 See Chapter XI. 3 Plantes associees, of Humboldt, 1807. 

 4 See Drude, 1905. 



