1914] Babcoclc: New Variety of Juglans 55 



Eocene, several in the Oligocene, upwards of twenty in the 

 Miocene, and about twenty-five in the Pliocene, several of the 

 latter being very close to, if not identical with, existing species. 

 These are what remain in the very imperfect geological record. 

 Doubtless many others existed. Now that aggregate mutation 

 is known to have occurred once in such a group, it is reasonable 

 to assume the occurrence of such major discontinuous variations 

 as one of the processes by which new species have been produced. 

 A recent effort^" to harmonize the older theories of evolution 

 through continuous variation and the modern conception of 

 alternative inheritance assumes that "unit characters" are really 

 composite in nature, but the paleobotanist will not necessarily 

 accept the hypothesis that all new species were built up from 

 such minute discontinuous variations that the effect is one of 

 continuous though gradual change. It is just as reasonable to 

 assume that the fossil species sprang into existence in the same 

 sudden manner as that by which quercina made its appearance. 

 On account of the persistent assumption by some^^ that 

 quercina is a natural hybrid between walnut and oak and that 

 the progeny of the original quercina trees are composed of walnut 

 and oak seedlings in Mendelian proportions, it should be noted 

 that there is wide variation among the fruiting specimens of the 

 new form as to the proportion of calif ornica and quercina seed- 

 lings they produce. I have tested seeds from three of the original 

 trees distributed by Disher^ and find they differ very widely in 

 this respect. They certainly produce no oaks and there is no 

 basis for assuming a Mendelian ratio among the progeny. 



