160 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



there develop offspring which in a few generations completely recover 

 their power of flight. 



Dr. Morgan rightly shows that individual or fluctuating variations 

 which oscillate about a mean or " mode " do not, as a rule, supply a basis 

 for new species ; because it is a sine qua non that all characters of a true 

 species must have hereditary constancy — relative, that is, as long as the 

 environment is constant — but Dr. Morgan omits this latter requisite. As 

 an example, variation in size of the leaves and flowers is one of the 

 commonest of fluctuating elements ; thus Ranunculus Ficaria has no 

 recorded varieties, but an abundance of individual differences in England. 

 In Malta, however, the leaf and flower are invariably much larger than in 

 Eugland ; hence they have become fixed characters and the plant is 

 known as var. calthafolia. 



Dr. Carl Pearson appears also to hint at a recognition of Darwin's 

 alternative, but includes selection, as in a quotation made by the author : 

 " If a race has been long under the same environment, it is probable 

 that only periodic selection is at work, maintaining its stability." No 

 " selection " really exists at all, as all individuals have grown in response 

 to the same climatal conditions. 



Dr. Morgan does not hesitate to criticise Darwin's theory severely ; 

 and he quotes Darwin's observations on " checks to increase," which runs 

 parallel with Malthus' " Essay on Population " ; but it is all really 

 beside the application of natural selection as applied to the origin of 

 species ; for specific characters depend entirely upon morphological 

 variations, i.e. in details of structure alone. Hence Dr. Morgan rightly 

 shows that "the struggle for existence only determines the Distribution 

 of Species," not their origins. 



Dealing with the Neo-Lamarckian school, he discusses the question 

 of the inheritance of acquired characters ; but, as the book is on 

 " Evolution and Adaptation," to refer to all the effects of experimental 

 mutilations and diseases, &c, seems to be entirely beside the question ; 

 for, even if such were inherited, they have no classificatory value, upon 

 which species entirely depend. 



Moreover, it is a question which is most easily answered by plants. 

 Thus, e.g., the tendrils of Ampelopsis hederacea (the Virginian creeper) do 

 not form adhesive pads until after contact is sustained with a wall ; 

 whereas in A. Veitchii they are already partially formed before, but only 

 completed after contact. Hence they are hereditary structures solely 

 induced by mechanical irritation of the soma. 



Again, roots of radish, as well as of turnip and rape, are globular or 

 elongated, according as the seed is sown in a compact or loose soil. Yet, 

 by selection, these features are now hereditary. Similarly, short and 

 long carrots were produced in the same way. Analogous cases can be 

 multiplied to any extent. 



Now, with regard to mutations, they are new species which are " all at 

 once there." The theory stands, therefore, in sharp contrast to the 

 selection theory of Darwin. They correspond to " sports " or Darwin's 

 " single variations." But the question is, what causes them to appear? 

 The author declines to enter into any discussion as to causes of mutation, 

 just as Darwin did for variations. The weight of experience proves that 



