CHAPTER XXI. 

 OONCLUDINa OBSERVATIONS. 



605.— The Number of Species of Plants. — It is impossible 

 at the present time to give with even approximate accuracy 

 the number of existing species of plants. In the first place, 

 a great many species in all parts of the world are as yet un- 

 described ; even in England, where the study of this branch 

 of Botany has been most energetically pursued, many new 

 species are discovered every year. In the central and western 

 countries of the continent of Europe, as in England, while 

 comparatively few flowering plants have escaped detection, 

 there yet remain undescribed hundreds of species of the 

 lower groups, and in the regions eastward there are douhtless 

 many phanerogams as well as cryptogams which have not yet 

 been enumerated. A complete "Flora of Europe" will 

 probably be an impossibility for very many years. In Asia 

 our knowledge of the plants is still more fragmentary. 

 Japan and India, with parts of Asia Minor, are the best 

 known botanically, but even in these regions our knowledge 

 is almost entirely confined to the phanerogams and higher 

 cryptogams. In Australia and the islands to the northward 

 and in Africa, there are enormous tracts which have not yet 

 been explored. In the New World, from Mexico southward, 

 the descriptions and enumerations of the native plants are 

 scattered through many works, not one of which approxi- 

 mates completeness even for comparatively small regions. In 

 North America, the "Flora of North America," begun forty 

 years ago, is yet unfinished, even for the flowering plants.* 



* " A Flora of North America," by Jolin Torrey and Asa Gray. Vol. 

 I., 1838-40. Vol. II. (in part), 1843. Eesumed under the title of "A 

 Synoptical Flora of North America," by Asa Gray, 1878. 



