CAUSES OF GENETIC VARIATION 227 



with expt. H. 700A, where, as the father was sig?iaticollis, having 

 the same recessive character, their appearance might have been 

 expected not to pass unobserved. The temperature in the 

 older experiment is, of course, not given with the great accuracy 

 used in the second, and it may have been higher still. The humid- 

 ity also was widely different. Still, in discussing the phenomena 

 we should expect some reference to the very remarkable and 

 closely cognate discovery which Tower himself had previously 

 reported in regard to the same species. 13 



The hesitation which I had come to feel respecting these two 

 publications of Tower's has been, I confess, increased by the 

 appearance of a destructive criticism by Gortner 14 who has ex- 

 amined the parts of Chapter III of Tower's book, in which he 

 discusses at some length the chemistry of the pigments in Lep- 

 tinotarsa and other animals. As Gortner has shown, this dis- 

 cussion, though offered with every show of confidence, exhibits 

 such elementary ignorance, both of the special subject and of 

 chemistry in general, that it cannot be taken into serious con- 

 sideration. 



Some observations made by Dr. D. T. MacDougal 15 have 

 also been interpreted as showing the actual causation of genetic 

 variation by chemical treatment. Of these perhaps the least open 

 to objection were the experiments with Raimannia odorata, a 

 Patagonian plant closely allied to Oenothera. The ovaries were 

 injected with various substances and from some of the seeds 

 which subsequently formed in them a remarkable new variety 

 was raised. This varying or mutational form was strikingly 

 different from the parental type, with which it was not con- 

 nected by any intergradational forms, and it bred true. It made 



" As to the interrelations of these three forms, Tower states (1906, p. 18) that 

 angusiovittata, which he reared from undecimlineala, is intermediate between it 

 and signaticollis. Compare Stal, "Monogr. des Chrysomelides," 1S62, p. 163; and 

 Jacoby, Biol. Centr. Amer. Celeopt., vi, Pt. 1, p. 234, PI. xiii, fig. 20; Tab. 41. fig. 

 15; ibid., Suppl., p. 253. All these forms are evidently very closely related, and 

 the delimitation of species is quite arbitrary. Jacoby indeed suggests that unde- 

 cimlineata may be a variety of decemlineata. 



14 Gortner, Amer. Nat., Dec, ion, XLV, p. 743. 



16 Mutations, Variations, and Relationships of the Oenotheras, Carnegie Institu- 

 tion Publication No. 81, 1907. PP- 61-64. 



