1913] Babcocic: New Form of Juglans 



SUMMARY 



1. A new form of walnut has appeared on seven separate occa- 

 sions among seedlings of at least three different trees of Juglans 

 calif ornica Wats. 



2. This form is sufficiently distinct from all other walnuts to 

 justify its recognition as a new species. But in all but one of the 

 germination tests of seeds from the original trees, some seeds have 

 produced plants resembling the species type in leaf characters. 

 Moreover, the form is exceedingly variable. These facts are good 

 reasons for describing the new form as a variety of J. calif ornica. 



II. ORIGIN OF THE NEW FORM— HYPOTHESES, 

 OBSERVATIONS AND EXPERIMENTS 



In studying the nature and origin of this new form of walnut, 

 three working hypotheses have been retained, and two other 

 hypotheses have been eliminated so far as my experimental work 

 is concerned. The latter hypotheses will be discussed briefly 

 before passing to the fuller consideration of the working hy- 

 potheses and the investigations connected therewith. 



One of the first possibilities suggested was that the new form 

 may be a "reversion to an ancestral type." The species is long- 

 lived and stump-sprouts freely. A few generations might extend 

 back to a time when a now extinct form existed in the same area. 

 It is a well-known fact that our present American species inter- 

 breed freely when growing near each other, and also breed w^ith 

 Juglans regia under similar conditions. Hence it is conceivable 

 that such an extinct form might have interbred with J. cali- 

 f ornica. According to Mendelian principles, some of the progeny 

 would be heterozygous for certain characters, which might be the 

 distinguishing characters of the new form. Such heterozygous 

 progeny, under favorable conditions, would continue to produce 

 both parent forms and more heterozygous individuals. It is 

 conceivable, then, that the few trees thus far known to exist, 

 which are giving rise to the new form, are such heterozygous 

 individuals, and that our new form is really a supposed extinct 



