146 Report S.A.A. Advancement of Science. 



There can be no doubt tliat tlie study of species has received a 

 powerful impetus from the doctrine of evolution, and that no other 

 rational explanation of affinities has been ottered ; but we must not 

 close our eyes to the fact that, except in the very broadest outline, a 

 phylogenetic classification has so far not been realised, at all events 

 not in botany. Tlie same author whom I have just quoted, M. Vuil- 

 lemin, says: " This is a goal at which we may aim without having the 

 slightest ilhision that we shall ever reach it, just as the polar star 

 guides the navigator, who never dreams of reaching it." 



It is now close on fifty years since Darwin published his Origin of 

 Species, a work which will live for all time. It made evolution the 

 keynote not only of all biological work, but forced it also on all 

 other branches of human knowledge. Yet the principle, by which 

 the origin of species was supposed by him to have been brought 

 about, is by no means generally admitted by those who make ques- 

 tions of this nature a close stud\'. " The origin of species by 

 means of natural selection " was first denied by those who could not 

 or would not believe at all in evolution in the organic world. Their 

 number has gradually decreased until nowadays they are, amongst 

 serious students, a negligible quantity; but, on the other hand, other 

 principles have from time to time been urged forward, principles which 

 either excluded natural selection by the survival of the fittest, or, at 

 all events, supplemented it. Amongst the former was Neo- Lamarck ism, 

 which stipulated the transnnssion of acquired characters, and lately 

 De Vries' mutation theory has found many adherents. 



The recent researches of Hugo de Vries have done a great deal to 

 bring the question of objective existence of species again into the 

 foreground. In fact, his mutation theory becomes unintelligible if 

 species are grading into one another without any definable limits. 

 It is not my purpose to examine his evidence \ery closely, but 1 must 

 «ay that, while I have to admit that much of liis reasoning is based on 

 sound evidence, I nnist hesitate in acknowledging with him that we 

 can see species arise, as it were, before our eyes. 



At one time it was thought that specific constancy was, at all 

 events, absent in many of the lower vegetable organisms, such as 

 bacteiia. Botanists, sucii as De Bar}^ and Marshall Ward, strongly 

 opposed this view. On the one liand, it was true that frequently 

 moj-phological differences between the various so-called species could 

 not b(! observed : while, on the other hand, many showed a wide range 

 both in morphological and physiological properties. 'J'he minute studies 

 of recent years have confirmed these facts as regards variation, while 

 the views as to the constancy of the species of bacteria have also 

 been confirmed. Thus Van Calcar fcnnid that the tubercle-bacillus may 

 have three different types of growth when observed in artificial cultures 

 without changing its specific nature. 



The doctrine of tlie specific constancy of bacteria was greatly 



