Fhenainenaof Variation and Geographical Distribution. 1<' 



review of the species of Cupitliferce. He finds that the best knowu 

 species of oaks are those which produce the most varieties and subva- 

 rieties, that they are often surrounded by a provisional species; and, 

 with the fullest materials at hLs command, two thirds of the species he 

 considers more or less doubtful. His general conclusion is, that "in 

 botany the loicest series of groups, sl'^vaeieties, varieties, and races, 

 are very badly limited; these can be groupedinto species a little less vaguely 

 limited, xchi'ch again can be formed into sufficiently precise ge>'EEA.'' This 

 general conclusion is entirely objected to by the writer of the article in 

 the "Natural HLstory Review," who, however, does not deny its appli- 

 cability to the particular order under discussion, while this very differ- 

 ence of opinion is another proof that difficulties in the determination of 

 species do not, any more than in higher groups, vanish with increasing 

 materials and more accurate research. 



Another striking example of the same kind is seen in the genera 

 Rtibus and Rosa, adduced by ^Ir. Darwin himself; for though the 

 amplest materials exist for a knowledge of these groups, and the most 

 careful research has been bestowed upon them, yet the various species 

 have not thereby been accurately limited and defijied so as to satisfy 

 the majority of botanists. 



Dr. Hooker seems to have found the same thiiig in his study of the 

 Arctic flora. For though he has had much of the accumulated mate- 

 rials of his predecessors to work upon, he continually expresses himself 

 as unable to do more than, group the numerous and apparently fluctu- 

 ating forms into more or less imperfectly defined species. 



Lastly, I will adduce ^Mr. Bates' researches on the Amazons. Dur- 

 ing eleven years he accumulated vast materials, and carefully studied 

 the variation and distribution of insects. Yet he has shown that many 

 species of Lepidoptera, which before offered no special difficulties, are 

 in realitv most intricatelv combined in a tangled web of affinities, lead- 

 ing by such gradual steps from the slightest and least stable variations 

 to fixed races and well marked species, that it is very often impossible 

 to draw those sharp dividing lines which it is supposed that a careful 

 study and full materials will always enable us to do. 



These few examples show, I think, that in every department of na- 

 ture there occur instances of the instability of specific form, which the 

 increase of materials aggravates rather than diminishes. And it must 

 be remembered that the naturalist is rarely likely to err on the side of 

 imputing greater indefiniteness to species than really exists. There L- 

 a completeness and satisfaction to the mind in defining and limiting 

 and naming a species, which leads us all to do so whenever we consci- 

 entiously can, and which we know has led many collectors to reject 



