1914] BabcocJc: New Variety of Juglans 53 



The origin of quercina is similar to those transmutations in 

 Lycopersicum* Gossypium,^ Nicotiana,^ and CEnothera,^ which 

 have been described as aggregate mutations as distinguished 

 from loss or addition of single characters as, for example, in 

 Eelianthus'^ and Drosophila.^ In regard to the tobacco mutation 

 above referred to, the authors*^ assume ' ' that mutation must have 

 taken place after fertilization, i. e., after the union of the male 

 and female reproductive cells." Castle** suggests it is equally 

 probable that the mutation occurred in an egg cell which then 

 developed without fertilization since "parthenogenesis is known 

 to occur in tobacco and mutation in a growing or immature germ 

 cell seems inherently more probable than in a fully formed and 

 fertilized one." This discussion is pertinent to both phases of 

 the problem herein set forth, viz., first, an explanation of the 

 variation found in the F^ oak-pollinated walnut seedlings ; second, 

 the cytological time of the mutations that produce quercina 

 seedlings. 



Concerning the first question, parthenogenesis or, more specif- 

 ically, apogamy, assuming the occurrence of reduction in chromo- 

 some number, might explain the variation in the F^ oak-pollinated 

 seedlings whereas such an extent of variation is too great to 

 permit the assumption that embryos developed from the spore 

 mother cell or other sporophytic tissue without also assuming 

 irregularities in chromosome behavior. Reduction is not assumed^* 

 in the classical cases of parthenogenesis in angiosperms {Ante'n- 

 naria, Taraxacum, Hieracium and Alchemilla) , but in Thalictrum 

 purpurascens Overton^^ finds "the development and germination 

 of the megaspore is that usually found among angiosperms." lie 

 reports no observations on chromosome behavior but shows that 

 "parthenogenesis is becoming fixed in Tlialictrum." In such an 

 instance it seems reasonable to assume that the omission of reduc- 

 tion has become established also. But in Juglans the existence 

 of adaptation for wind pollination would indicate that pollination 

 and fertilization are usually essential for seed production and 

 there is experimental proofs of this also. Moreover, the extensive 

 researches of Nawaschin and Finn^- on the cytology of fertiliza- 

 tion in Juglans, although lacking the treatment of chromosome 

 number and behavior, demonstrate that the process of fertiliza- 



