XlXviii PEOCEEDINGS OF THE 



different conditions to have independently produced distinct but 

 similar species, by acting on organisms which had not been one and 

 the same species ; but what else they may have been he seems to 

 think beyond the reach of plausible conjecture. 



Leaving, however, these questions of origin aside, he strongly ob- 

 jects to the classing representative with identical species in con- 

 sidering geographical disti'ibution ; for the former appear in such 

 absolutely dissevered distant regions that an interchange of species, 

 even in early geological periods, seems impossible, as, for instance, in 

 the case of several Ericas of the Cape and of Europe. It is on the 

 contrary, he believes, almost always possible to deduce the actual 

 progress of identical species from the form or phj'sical accidents of 

 their homes and from the means of dispersion at their command 

 (p. 519). He therefore, in combating Asa Gray's conclusion, com- 

 mences by eliminating from his calculations, after the example of 

 Miquel (" Over de Yerwantschap der Flora van Japan met Azie en 

 Noord America," in Yersl. K. Akad. Amsterdam, ser. 2, ii.), aU re- 

 presentative species, thus reducing Asa Gray's list of concordant 

 races in Japan and eastern North America from 226 to 81 ; from these 

 Grisebach subtracts 41, which are also inhabitants of western North 

 America, and can still, he thinks, daily transmit their seeds, across 

 the Pacific Ocean; 17 more are, in his opinion (supported by that of 

 other botanists), either certainly not identical or doubtful, and to be 

 added to the already eliminated representative species. Of the re- 

 maining 23, he finds 21 which can bear a high northern climate and 

 may yet be found in the Oregon or other imperfectly explored terri- 

 tories of North-west America ; and the whole long list is thus re- 

 duced to two species only, whose problematical disseverance in 

 Japan and Eastern North America remains unexplained, — the one, 

 Elodea petiolata, being a marsh plant, which as such possesses great 

 migratory powers ; the other, Carex rostrata, from the White Moun- 

 tains, awaits further researches on its geographical distribution. Even 

 admitting the possibiUty of the greater early dispersion of these 

 species in former geological periods propounded by Asa Gray, Grise- 

 bach thinks that any such great antiquity of the Japanese flora is 

 not estabhshed on so firm a ground as to supersede any attempts at 

 finding other explanations limited to the results of forces still in 

 activity in present times, and that accordingly the distribution 

 of the species in question may be satisfactorily accounted for by 

 the means of dispersion still available, if the data are viewed in the 

 light he has placed them in. I should doubt, however, whether his 

 mode of cutting up a long array of ascertained facts further increased 



