PLANT COMMUNITIES AND FLORAS. 



been dwarfed by peculiar circumstances to the level of low forest. If the uncon- 

 genial conditions referred to were to cease, a forest with standard-stems would grow 



up on the spot. 



III. Plains. The dominant plants are perennial and profusely-flowering herbs 

 and undershrubs of gregarious growth. The form, direction of growth, and mode of 

 ramification of the aerial herbaceous stems is always conspicuous, and may even be 

 recognized when the foliage-leaves are of considerable size. Innumerable grades of 

 this form of plant-community exist between Thistles and Umbellifers, reaching a 

 height of 2 metres, which flourish on the Steppes, and the undershrubs scarcely 

 2 centimetres high, which grow on the debris-slopes in high mountain regions. No 

 sharp line of demarcation can be drawn between them. Nor can any exact distinc- 

 tion be maintained between those Plains in which annuals and biennials and those 

 in which perennial growths predominate. It is, however, possible within certain 

 limits to distinguish between the different types of vegetation under this heading. 



IV. Another type, which may be termed the frondose type, has as its dominant 

 plants such as have their stems either entirely subterranean, or else rising but 

 slightly above the ground, whilst from their extremities are developed a crowd of 

 fronds, branch-like leaves, or leaves with large laminae. The stems are completely 

 hidden by these leafy structures, so that their form and direction and the nature of 

 their ramifications are never clearly visible. This type is conspicuously wanting in 

 flowers. Where flowering-plants also form a constituent part, such plants either 

 have precocious flowers, which have already passed into the fruiting stage by the 

 time the mass of foliage has unfolded, and which subsequently disappear without 

 leaving any trace (e.g. Saxifraga peltata, Tussilago, Petasites), or else their flowers 

 are so lost amid the innumerable large foliage-leaves that they do not occasion any 

 material alteration in the general aspect of the plant-community (e.g. Funkia, 

 Ndumbium] see fig. 436, p. 775, and most Aroideae). A special form of this type is 

 exhibited on the surfaces of stagnant or gently flowing water, where discoid foliage- 

 leaves rest upon the water and cover the surface completely. Of it there are several 

 varieties depending on the dimensions of the constituent parts; c/., for instance, 

 Water Lilies and Duckweed. 



V. Ribbon-growths. The dominant plants are social hydrophytes with submerged 

 stems and foliage-leaves, or with stem-like or foliaceous thaUi. Sometimes forms 

 possessing foliaceous thaUi and long, flaccid, ribbon-shaped foliage-leaves predo- 

 minate, sometimes forms which look like submerged leafy or leafless shrubs, but 

 which differ from real shrubs in that they are herbaceous throughout. A gregarious 

 rowth of species with thaJi or foliage-leaves which are split up into long narrow 

 igments, or of species whose thalli exhibit a whorled system of ramification may 

 be present. Ribbon-growths may be separated into various subdivisions 

 *ording as one or other of these different sorts of plant predominates. 



-The type is afforded by plants which grow in quantities together 



herbaceous stems of the kind called haulms and scapes. The stems are 



foliage-leaves (Horse-tails, Rushes, &c.), or else they bear long, narrow 



