TYPES OF PLANT-COMMUNITIES. 889 



leaves. Shoots bearing inconspicuous flowers spring up from the species which 

 grow in tussocks, whilst the non-tussoek-forming, but more continuously crowded 

 types, develop haulms and scapes bearing an abundance of leaves. The tufted 

 sedges afford an example of the former, and arundinaceous plants of the latter. A 

 reed-like vegetation is developed both on marshy and on dry ground; instances of 

 the latter occur in the Tropics and in Steppe-regions. 



VII. Carpet— ThQ typical character is given by low, perennial plants, which 

 form a close mat covering the ground. According as plants with narrow, stiff, 

 grass-like leaves predominate, or such as form a soft, swelling carpet, two types 

 may be distinguished; further, according to the nature of its most important 

 constituents the community may be spoken of as a grass-carpet, herbaceous carpet, 

 moss-carpet, &c. Carpets may grow either on dry or on marshy ground. Sometimes 

 they are restricted to the immediate vicinity of springs or form merely a coating to 

 slabs of rock, but they also spread over wide areas on mountain-slopes and basins. 

 They belong especially to high mountains and to the Arctic regions. 



VIII. Incrustment. — The dominant species are Thallophytes, which become 

 rigid and brittle when dry or as a consequence of being incrusted with lime. The 

 aggregations of these plants either form solid banks and reefs or else spread in the 

 form of a loose covering over the earth, or they appear as incrustations on rock, 

 earth, or sand. They develop both in the air and under water. 



IX. Felts. — The dominant species are plants possessing thalli composed of 

 delicate filaments which are more or less entangled together. They may grow in 

 water either in a flocculent form or in coherent felted masses, and they also appear 

 as a thin coating to stones or earth, in which form their characteristic colours render 

 them visible from afar. 



The names applied to the above nine classes or types of plant-communities are 

 purposely devoid of reference to the particular alliances, families, or genera 

 concerned in the formation of the communities, because the origin of the latter 

 has nothing to do with the existence of any affinity amongst their constituent 

 plants. Nor has it been possible to take into account the nature of the habitats or 

 the situation of the zones and regions of the earth's siu-faee where the communities 

 grow. This is not the case, however, when we come to name the separate com- 

 munities which belong to the above classes. For this purpose the use of a name 

 which refers to the habitat, zone, or region where the particular community 

 flourishes, or to the ruling species, genera, or families of which it is composed, is 

 not only inevitable but actually desirable. The most convenient system of nomen- 

 clature to adopt here is that which has proved the best in all other descriptive 

 sciences. In accordance therewith each plant-commimity is designated by two 

 names, one denoting the class to which the community belongs and the other 

 indicating its special characteristics. 



In the present state of our knowledge it is impossible to name even approxi- 

 mately the plant-communities which are formed by the aggregation in various 

 ways of some or other of the many thousands of species inhabiting the earth. I 



