1 University of California Publications in Agricultural Sciences | \'o]. 2 



form, wliose existence is revealed through sewreo-ation of unit 

 characters in tlie o;ametes of the heterozygous individuals. But 

 this conception was unsatisfactory as a present working- hypo- 

 thesis, since it necessarily assumes a parent form, the existence 

 of which can only be proved by paleontological records. So far 

 as the writer has been able to ascertain, none of the extinct species 

 of Jnglans or Carya thus far described resemble the new form 

 in number and shape of leaflets and proportionate size of lateral 

 and terminal leaflets.* Herbarium material of other related 

 genera has also been examined to see whether a suggestion of 

 the new form's leaf characters could be found, but without suc- 

 cess. However, until some other hypothesis is proved to fit the 

 case, this one should be reserved as having some value. 



Another possibility is that the new form is a hybrid between 

 Juglans californica and some other species, such as J. regia or 

 J. nigra. This suggestion has not been used as a working hypoth- 

 esis because the characters of hybrids between these two species 

 and J. californica are already known. It is generally understood 

 that plants of the Fj generation of both these crosses reveal 

 the partial dominance of J. nigra or J. regia as the case may be.^ 

 They always have larger leaves than those of J. californica, 

 whereas our new form is characterized by its small leaves. It 

 is hardly conceivable, then, that the new form is the direct result 

 of such a cross, nor even that the wild trees from which our new 

 form springs could belong to the Fj or a later generation from 

 such a cross and thus produce the new form among the extreme 

 variations that sometimes occur among the younger generations 

 of hybrids between species. For our new form is the only 

 extreme variation which has been reported among the many 

 thousands of /. californica seedlings that are grown annually in 

 California. Moreover, J. regia has been cultivated in southern 

 California for less than fifty years, while only a few cultivated 

 trees of J. nigra occur, and these also came witli the introduction 

 of commercial walnut growing. Other known species of Juglans 



^ Dr. W. A. Berry, in a letter to the writer, expressed the following 

 opinion: "I suspect if a paleobotanist liad come across such a form, and 

 I know of none such, lie would have thought of the Anacardiaceae rather 

 than Juglans." 



■'•■Smith, R. E., "Walnut Culture in California," Univ. Calif. Agr. Kxp. 

 Sta. Bull. 231, pp. ] 57-1 70. 



