22 University of California Publications in Agricultural Sciences [\o\. 2 



12. figure 19, is from a photograph of tree No. 16 taken in April. 

 1913. About four Inmdred twigs on this tree likely to bear nuts 

 have been covered so as to insure self-pollination. In this \va\- 

 it is hoped to locate the twig or twigs producing mutants. 



The data at hand indicate that the new form is not a typical 

 mutation fi'())ii the seed in the usual meaning of tluit expression. 

 All ])nt one of the tests of the seeds from the original trees have 

 revealed a partial reversion to the species type in the second 

 generation (counting Disher's original trees as the first genera- 

 tion). Now, one of the generally accepted distinguishing char- 

 acteristics of a mutant is that it breeds true from the first. Imt 

 here is a remarkably distinct form w'hich does not breed true. Of 

 course, this should not exclude the possibility of origin by muta- 

 tion of an " eversporting variety." It is (piite possible that 

 qnercina is an eversporting variety and. if so. it may .still have 

 originated without an antecedent hybridization, but would then 

 never breed true.^^ However, it does not appear to the writer 

 that the term "eversporting variety" as used by De Vries is 

 applicable to this form. De Vries classes as eversporting varieties 

 such inconstant forms as striped flowers, five-leaved clovers, and 

 polycephalic poppies. But in this new walnut, we have a form 

 which is distinct in most of its characters from the parent form 

 and which breeds true in a portion of its offspring, the remaining 

 portion showing complete resemblance to the parent form. 



It has been suggested by Professor H. B. Torrey that muta- 

 tions may occur in the gametes of one sex while the gametes of 

 the other sex are normal and, hence, that the new form appears 

 among first generation seedlings, but fails to l)reed true in the 

 second generation. 



Some doubts as to Professor Torrey 's suggestion arise when 

 we consider the results of a pollination experiment which the 

 writer made in 1908. Pollen from Disher's original non-fruiting 

 tree was placed upon pistillate flowers of Tree I. referred to in 

 the discussion of the first hypothesis. All of the eleven seedlings 

 growing from this cross resemble Jinjlnns californica. On the 

 basis of Professor Torrey 's suggestion, this would be explained 



■1 Dr. George H. Shiill kindly suggostoil the exiilaiuitinn mi tlic b;isis 

 tliJit qnercina is an eversporting variety. 



