32 THE ORIGIN OF GYNANDROMORPHS. 



These cases are not to be confused with mutation in the germ- 

 tract, where, in a sense, the reverse situation is realized, for while in 

 Drosophila the mutation of a sex-linked character in one female chromo- 

 some appears immediately in one (or more) of her sons, the mutation 

 itself occurred first in the female. Conversely, in moths, if a germ- 

 tract mutation took place in the male it would show immediately in 

 one or more daughters. The well-known case of Abraxas grossulariata 

 may be taken to show why mutation taking place in a male is expected 

 to show first in the female and not in the male offspring. The genetic 

 evidence for Abraxas indicates that the female has one sex chromo- 

 some, the male two. The aberrant form lacticolor is found occasion- 

 ally in nature and is always female. A mutation to lacticolor in a 

 Z chromosome of the male would give rise to a daughter if this sperm 

 fertilized a not-Z egg that would at once show the sex-linked character 

 lacticolor. 



MOSAICS IN PLANTS. 



The cause of variegation in plants is too involved and obscure 1 

 to attempt to discuss in this connection. On the other hand, the 

 occurrence of bud-sports is generally recognized as due to somatic 

 mutation which may include the germ-tract also. The frequent occur- 

 rence of bud variation in the cultivated forms of the foliage plant 

 Coleus has recently been studied by Stout, who has obtained from a 

 single plant (and its clones) a number of types differing both in color 

 and form of the leaves. The cultivated varieties have arisen through 

 hybridization. Three interpretations suggest themselves as possible. 

 Elimination of the chromosomes of the hybrid might account for the 

 results, but no information as to the chromosomes in the different 

 types is available. If any of the colors are due to cytoplasmic plastids, 

 their irregular distribution might also be responsible for the result. 

 Thirdly, the change might be due to a mutation. If the types studied 

 are complex hybrids with one or more heterogeneous pah's of chromo- 

 somes, a change in one gene of one chromosome might bring about 

 directly a visible change in the color. Until more critical Mendelian 

 work is done it is not possible to reach any plausible or even probable 

 conclusion. It might be possible to analyze the results more closely 

 if we knew what kinds of offspring arise from the original plant and 

 its varieties. Owing to the complex nature of the plants this pro- 

 cedure offers difficulties. A few facts are given by Stout. He states 

 that "plants grown from seed give wide variations .... Many 

 of the types that had appeared as bud variations appeared also in the 

 seed progenies. " 



Winkler produced mosaics by grafting tomato and nightshade, which 

 are now supposed to be due to a combination of the tissues of the 



1 Except in the case of Pelargonium and of Mirabilis, where Baur and Correns have shown 

 that the mosaics are caused, in some instances at least, by plastid assortments. 



