- [Footnote: may he further elucidated and illustrated by the following
analogous considerations.
The major part of the Compositæ, of which Linnæus knew only 785 species and which has now grown to 12000, appear to belong to the Old Continent: at least Decandolle described only 3590 American, whilst the European, Asiatic, and African species amounted to 5093, This apparent richness in Compositæ is, however, illusive, and considerable only in appearance; the ratio or quotient of the family, (1/15 between the tropics, 1/7 in the temperate zone, and 1/13 in the cold zone), shews that even more species of Compositæ than Leguminosæ must hitherto have escaped the researches of travellers; for a multiplication by 12 would give us only the improbably low number of 144000 Phænogamous species. The families of Grasses and Cyperaceæ 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 Gramineæ. If we had sufficient grounds for be-*]*
