56 University of California Publications in Agricultural Sciences [Vol. 2 



SmiMARY 



1. The belief, which has been held by many, that the new 

 form of walnut, Juglans californica var. quercina, originated 

 through hybridization between walnut and oak is without founda- 

 tion in fact. There is no evidence that hybridization with other 

 species of walnut or cross-pollination with other trees of the same 

 species causes the appearance of the new form. 



2. Although abnormal, late appearing flowers and fruits oc- 

 cur rather frequently on the California Black Walnut, only one 

 tree has been found to produce abnormal nuts which give rise to 

 quercina seedlings, and more than half of the abnormal nuts from 

 this particular tree produce typical californica plants. Certainly 

 teratology cannot be considered the cause of the origin of the new 

 variety. 



3. The evidence that seedlings of the new variety come from 

 certain apparently normal nuts is conclusive, since a tree has 

 been located that annually produces a small percentage of quer- 

 cina seedlings. Evidently these aberrant individuals are the re- 

 sult of internal changes that take place during the growth of the 

 flowers previous to fertilization. It is possible that evidence of 

 these changes will be discovered by microscopical study of 

 material from tree no. 16 and that further breeding experiments 

 will help to explain them. Meanwhile, whether the true nature 

 of these changes be revealed or not, we know that embryos are 

 produced independently of the influence of self- or cross- 

 pollination, which are capable of developing into individuals pos- 

 sessing characters strikingly different from those of the parent 

 and capable of transmitting those same characters to at least a 

 portion of their progeny. Such occurrences of discontinuous 

 variation are generally recognized as mutations, and the quercina 

 walnut is similar to certain mutations in tomato, cotton, tobacco 

 and evening primrose, which have been designated as aggregate 

 mutation. 



Transmitted June 15, 1914. 



