344 ANNUAL OF SCIENTIFIC DISCOVERY. 



" Supposing all the flowering plants cultivated at one time in all the botanic 

 gardens of Europe to amount to 20,000, and assuming from the foregoing 

 comparisons that the cultivated speeies amount to about the eighth of those 

 described and preserved in collections, the latter would amount to 160,000 

 species. Large as this number is, it will scarcely be thought excessive, 

 when we recollect how small a proportion of many large Orders are to be 

 found in our gardens, scarcely l-100th part, for example, of the Guttiferaj, 

 Malpighiacece, Melastomacese, Myrtaceae, and Rubiacese. 



" If we apply this mode of calculation to the number of species given by 

 Loudon (26,660), the estimate of 160,000 rises to 213,000 species." 



These deductions, based upon Kunth's inferences, refer to the species that 

 have been described, and are now existing in herbaria. It remains to esti- 

 mate the whole number of species upon the globe, judging by the proportion 

 under the cultivation of art and the examination of science. The following 

 statement exhibits the principle on which the calculations are based: 



" Walpers' ' Repertorium/ supplementary to De Candolle's ' Prodromns,' 

 brings the number of Leguminosae up to 8068 species in 18 16. The propor- 

 tion of the number of the Leguminosai to that of the entire Phanerogamous 

 flora is l-10th within the tropics, l-18th in the temperate, and 1-35 in the 

 north frigid zone; so that Ave may assume the mean proportion of this fam- 

 ily to be l-21th. The 8068 described Leguminoso3 would therefore lead us to 

 suppose that there existed only 169,400 species of flowering plants upon the 

 surface of the globe, whereas the Composite, as stated above, indicate, by 

 Kunth's mode of deduction, more than 160,000 already known species. 



" Of the Composite, Linneus was acquainted with only 78-3 species, while 

 10,000 are now known. The greater part of these appear to belong to the Old 

 World, De Candolle describing only 3500 American, with 5093 for Europe, 

 Asia, and Africa. But this seeming abundance of the Composite is to a 

 certain extent deceptive and only apparent. The proportions of this Order 

 are l-15th between the tropics, l-7th in the temperate, and l-13th in the 

 frigid zones, giving a mean of l-12th, which shows that even more species of 

 Compositor than of Leguminosae have escaped investigation hitherto, since a 

 multiplication by 12 Avould give us the improbably low number of 120,000 

 Phanerogamia. 



" The Grasses and Cyperacese give still lower results, as comparatively fewer 

 still of these have been collected and described. The mean proportion of 

 the Grasses seems to be about l-12th. Taking the number of known spe- 

 cies of plants according to the above calculations at 160,000 or 213,000, the 

 Grasses ought to amount to 13,333 in the first case, and 17,750 in the second, 

 while only either l-4th or l-5th of these numbers is known. When we 

 reflect what enormous extent of plain still remains unexplored in almost all 

 parts of South America, and in Northern and Central Asia, this deficiency 

 does not appear extraordinary ; and, indeed, it becomes by no means diffi- 

 cult to believe that we are so deficient of knowledge of species of Grasses, 

 that the total number of flowering plants might be taken at double the num- 

 ber known, which would lead to the conclusion that only l-8th or l-10th of 

 the Grasses had as yet been discriminated." 



ON THE GROWTH OF PLANTS. 



At the Dublin meeting of the British Association, Prof. Buckman, from 

 the committee appointed to experiment " On the effect of external con- 



