I'JKH] Babcock: New Form of Jugluns 21 



Third Hypothesis 



The possibility that the original trees of the new form are 

 mutants has been recoonized from the first. If it can be shown 

 that the recurrence of this form among seedlings of Juglans cali- 

 f arnica trees is due to repeated mutations in certain individuals, 

 this W(Mild be good evidence that the original trees were similarly 

 produced. The rejietition of mutations is not contrary to experi- 

 (niec but i-ather is characterstic of species known to l)e in a 

 mutating period. It is generally admitted that plants exhibiting 

 the evidence of being in a mutating period are rare. "Hugo de 

 Vries admet I'hypothese d'une unitabilite periodique et rare" 

 (Blaringhem). Amon-j the plants reported ;is l)(Mng in sucli an 

 abnormal condition, the number of trees is very small. Hence 

 the phenomena connected with the occurrence and recurrence of 

 this new form of walnut gather increased interest as soon as 

 the hypothesis of origin by mutation is considered. 



The chief obstacle to adequate investigation based on the 

 hypothesis has been the difficulty in locating a single tree of 

 Juglans californica from whose seeds the new form is known to 

 grow. With such a tree located under conditions favorable to 

 experimental work, a careful study of its vegetative and repro- 

 ductive parts can be made and pollination may be controlled. 

 After several years of searching such a tree has now been located. 

 It is a certain tree in the Garden Grove row of black walnuts^" 

 from which nuts have been gathered by nurserymen, who have 

 found seedlings of the quercina type during a period of several 

 consecutive years. 



In 1912 I had the nuts from twenty-one of the trees in this 

 row gathered separately, lalieled with numbers corresponding to 

 numbers attached to the trees, and shipped to Berkeley. These 

 were soaked, planted in sand in flats, properly labeled and placed 

 under the benches of a glass house, in February, 1913. Two 

 months later, six (/ik i-ciiia seedlings were found in the flats from 

 tree No. 16. There were 275 seedlings in all. Thus slightly over 

 two per cent of the seedlings secured from the 1912 crop of this 

 tree appear to be mutants. Plate 11, figure 18, shows one of 

 these seedlings and one normal seedling from tree No. IG. Plate 



1" Cf. Recurrence of tlie New Foini, \>. •"). 



