322 WILLIAM LAWRENCE TOWER. 



sort of hybridization behavior. I am of the opinion that Bate- 

 son's suspicion is probably justified, at least in some instances. 

 I have no experience with plants and especially none with (Eno- 

 thera Lamarckiana, but my experience with these synthetic exper- 

 iments has suggested that the type of behavior which DeVries 

 has discovered, and upon which he has built an all-inclusive 

 theory of evolution, is in reality nothing more than the reap- 

 pearance from time to time of attributes brought into a strain 

 by hybridization, and which reappear in every generation, 

 or in frequent generations, by some process akin to Mendelian 

 segregation. 



It seems unreasonable to advance, as has DeVries, the idea 

 of a pre-mutation period, with a gradual development of invis- 

 ible pangenes, and then a final bursting of these pangenes 

 into a full-fledged mutation period, followed by a gradual dying 

 away of the mutation period which leaves a species in a condi- 

 tion in which it does not produce these sports. Rather, the 

 explanation which Bateson suggested, and which I have shown 

 to be capable of creation in these synthetic experiments, is far 

 more plausible and more likely to be the real explanation of the 

 type of behavior found. 



This raises a very large question — one that has been 

 raised many times — as to whether natural species may not 

 be hybridization complexes rather than pure line cultures 

 isolated by some sort of selection, as has been presupposed since 

 the time of Darwin. I have found that in nature, crossing, es- 

 pecially between these chrysomelid beetles, is by no means un- 

 common, and very frequently results in adult progeny in nature, 

 some of which have been described as species. These natural 

 cases of hybridization have been observed in the last half dozen 

 years along the edge of the Mexican plateau. Some other species 

 of chrysomelids from the same general region, especially some 

 species of Labidomera, have a variability strongly suggestive of 

 a similar origin. I have found that Labidomera suturella Chevr., 

 of which many sharply marked variations have been described, 

 gives a variability in pedigreed cultures that is strongly suggestive 

 of the species having arisen through a process of hybridization. 

 On the high volcanic plateau of Toluca there is another type 



