THE MUTATION THEOEY. 



175 



THE MUTATION THEOEY: 

 A OEITIOISM AND AN APPEEGIATION. 

 By Eev. Peofessor G. Henslow, M.A., F.L.S., V.M.H. 



This important volume,''' consisting of 674 pages, with numerous 

 illustrations in the text and six coloured plates, is a great fund of facts, 

 inferences, and conclusions, and speaks volumes for the author's en- 

 thusiasm to discover Nature's laws, coupled with immense painstaking 

 in experiments and observations. 



It is divided into three parts: I. The Origin of Horticultural 

 Varieties. II. The Origin of Eversporting Varieties. III. The 

 Eelations of the Mutation Theory to Other Branches of Inquiry. 



In previous notices of Prof, de Vries' two books — Species and 

 Varieties: their Origin by Mutation,"! and " The Mutation Theory," 

 Vol. l.l — I pointed out that the work did not appear to advance any- 

 thing new to science, but only added to the nomenclature. Mutations 

 stand for some uncertain amount of variation, greater than the usual 

 fluctuating variations seen in individual differences." The latter are 

 mostly trivial, such as between the peas in a pod, slightly different 

 shapes and sizes of leaves on one and the same tree, etc. These Wallace 

 regards as merely " non-specific or developmental characters. "§ 



As a rule they have no permanent value, since they are due to local 

 and temporary differences in their degrees of nourishment. But, if 

 any such happen to become constant by heredity, it may be utilized as 

 a systematic variety or " elementary species " or " mutation." Such, 

 for example, are the numbers of black dots on the petals of species of 

 Hypericum, which are mentioned by systematists as diagnostic 

 characters. Similarly the four petals instead of five is a specific 

 character in Tormentil. Again, if a plant be accidentally half-starved, 

 it will readily recover itself with more water; but let it remain for 

 generations in the same poverty-stricken conditions its ** starvation- 

 characters " will become fixed and hereditary, so that it will perhaps 

 come to be named depauperata ; such may be seen in Sagina apetala, 

 Nardus stricta, &c. 



The theory of mutations as advocated by Professor de Vries is often 

 referred to as something new, and as an alternative to Darwin's; but 

 Mr, Th. Meehan, of Germantown, Philadelphia, advocated the same 

 thing nearly forty years ago. His paper|| begins: Natura non 



* The Mutation Theory. Experiments and Observations on the Origin of 

 Species in the Vegetable Kingdom. Vol. II. The Origin of Varieties by 

 Mutation. By Prof. Hugo de Vries. Translated by Prof. J. B. Farmer and 

 A. D. Darbishire. viii.+674 pp. (Kegan Paul, Trench, London, 1911). 18s. 

 net. 



t Journ. Roy. Hort. Soc, xxxi. 1907. t Idem., xxxvi. 1910. 



§ Fortnightly Review, 1895, p. 44. 



II Proc. of the Amer. Assoc. for the Advancement of Science, 1874. 



