120 PHYSIOGNOMY OF PLANTS. 



may be further elucidated and illustrated by the following 

 analogous considerations. 



The major part of the Composite, of which Linnaeus knew 

 only 785 species and which has now grown to 12000, 

 appear to belong to the Old Continent : at least Decandolle 

 described only 8590 American, whilst the European, Asiatic, 

 and African species amounted to 5093. Tin's apparent 

 richness in Compositse is, however, illusive, and considerable 

 only in appearance ; the ratio or quotient of the family, 

 (-yV between the tropics, -f in the temperate zone, and T ' T in 

 the cold zone), shews that even more species of Composite 

 than Leguminosse must hitherta have escaped the researches 

 of travellers; for a multiplication by 12 would give us only 

 the improbably low number of 144000 Phsenogamous 

 species. The families of Grasses and Cyperacese give still 

 lower results, because comparatively still fewer of their 

 species have been described and collected. "We have only 

 to cast our eyes on the map of South America, remembering 

 the wide extent of territory occupied by grassy plains, not 

 only in Venezuela and on the banks of the Apure and the 

 Meta, but also to the south of the forest-covered regions of 

 the Amazons, in Chaco, Eastern Tucuman, and the Pampas 

 of Buenos Ayres and Patagonia, bearing in mind that of 

 all these extensive regions the greater part have never been 

 explored by botanists, and the remainder only imperfectly 

 and incompletely so. Northern and Central Asia offer an 

 almost equal extent of Steppes, but in which, however, 

 dicotyledonous herbaceous plants are more largely mingled 

 with the Graminese. If we had sufficient grounds for be- 



