642] NATURE OF BUD VARIATIONS * 77 



transition regions between the green and the pale-green 

 areas, the cells contain not only green and colorless plas- 

 tids, but all intermediate conditions as well. Since the 

 green and the white plastids are not two sharply differen- 

 tiated kinds, but are the end members of a continuous 

 series arising from minute primordia which, so far as can 

 be seen, are of one kind, he regards any simple form of 

 segregation hypothesis as inadequate. It seems possible, 

 however, that these primordia may be functionally, even 

 though not morphologically, of two more or less distinct 



Graft -hybrids and Other Chimceras.—Uhe well-known 

 graft-hybrids of Solanum reported by Winkler are of 

 interest from the standpoint of this discussion because of 

 the bud variations commonly exhibited by them. Sec- 

 torial chimaeras, produced by adventitious buds arising 

 from the point of union of stock and scion of grafts of 

 tomato and nightshade, and ]i;in inu- one side of tlic one 

 species and the other side of the otlici-. lia\i' not infi'c- 

 quently later produced branclu's that wwv pciirlinal 

 chimaeras having tissues of one >|)*cic> enclosed within an 

 envelope of the other. Tlnit thoe hi-anrhe- are really 

 periclinal chimaeras has been e>tal)lishe( 1 chroniosome 

 counts and by the fact that seedlings pi-odure.l l.y them 

 are always of the species of the subepid* rnial ti<sne from 

 which gametes arise. These periclinal ehint:eias in tnin 

 have been observed to produce brandies \vlioll\ o!' one oi- 

 other of th(> ])arent s])eeies. The marked .li flVivn,-.- in 

 appearance between the sectorial and periclinal cliima'i'a- 

 and between tiie latter and either parent speri,.> placr> 

 this behavior clearly in tlu" class ot' bnd \ariation and, 

 since the production of branches of the i)ai-ent spiries 

 from periclinal chimaeras is the lesnlf of a reparation of 

 genotypes that were closely nnited pi-evion>l\ . the |)]ie- 

 nomenon is perha])s i-ightl\' classed a- a form of veu'eta- 

 tive segregation. It is oh\ ions, liowe\ cr, that the >c])ara- 

 tion of tissues that are niei-ely clo>el\ a-s(»cialc(l in the 

 graft hybrid is a fundamentally diffeivnt type of -ei^re- 

 gation from that by which tln^ chi-omosonK's or even the 



