K.— BOTANY. 233 



leaps, an evolution in harmony with the uniformitarian principles estab- 

 iished by LyelL' But he remarks that he does not favour any exaggerated 

 ideas such as the so-called ' omnipotence of natural selection.' 



In the present year Professor Graham Kerr, in his volume on ' Evolu- 

 tion,' also adopts a distinctly Darwinian position, but with greater stress 

 laid upon the potency of natural selection ; this might be expected from 

 •one who spent same of his most impressionable years in the wild surround- 

 ings of the Gran Chaco. He speaks from experience of the effect of selec- 

 tion as being ' in actual fact enormous,' and he holds that the attempts 

 that have been made to minimise its importance are to a great extent 

 fallacious. He sees in the recognition of Mendelian inheritance that the 

 natural-selection theory has been greatly fortified since Darwin's day. 

 Variability, upon which the theory depends, he regards as an expression 

 of that instability which constitutes one of the inherent and most character- 

 istic features of living substance, and he states that such variation has to 

 be accepted as a basic fact. He further regards as an added strength 

 to the Darwinian theory ' the recognition that a particular variation is 

 the outward expression of a tendeiicy to vary in that particular direction, 

 and that as a consequence the selection of variations in a particular direc- 

 tion involves a necessary intensifying of the tendency towards that 

 particular variation, and in turn the encouragement of evolutionary pro- 

 gress along a definite directed line.' These expressions are in general 

 accord with the doctrine of Weismann that acquired characters, or, as 

 Graham Kerr terms them, ' impressed ' characters, are not themselves 

 inherited. It is not for a botanist to interfere with the arguments of 

 zoologists on this question, as applied in their own science. There are, 

 however, zoologists who strongly maintain their belief in such inheritance, 

 a position upheld by Professor MacBride in the volume on ' Evolution ' 

 published last year by Messrs. Blackie, which is the third of the works above 

 mentioned. 



In that same volume I took the opportunity of stating that the question 

 of the origin of heritable characters, or mutations as they are called, is 

 still quite an open one for plants. But it was maintained that a wide 

 latitude of time is a real factor in the problem. This was already recog- 

 nised by Hofmeister, who on the last page of his ' AUgemeine Morphologic ' 

 said : ' It appears to me probable that only gradually, in the course of 

 many years' development, the influential effects on outer form appeared 

 and became hereditary.' Thus Hofmeister contemplated a slow inherit- 

 ance of acquired or impressed characters in plants. To anyone who notes 

 how directly susceptible individual plants are to external conditions, and 

 how greatly these affect their individual form, it would seem improbable 

 that there should be any sharp line of demarcation between the individual 

 and the racial life, or that what affects every individual plant so pro- 

 foundly should never affect the race. In my essay in Messrs. Blackie's 

 volume on ' Evolution ' I advanced comparative evidence, which commends 

 itself to my own mind as a raorphologist, indicating that the boundary 

 between fluctuating variations and heritable mutations is not absolute : 

 in fact that in plants, given latitude of time, variations related causally 

 with external circumstance, and not merely initiated at random, are 

 liable to be transmitted to the offspring. There is no need to repeat the 



