340 



THE GERM-PLASM 



bination of the characters of the two ancestral species con- 

 tinually varies in this plant, which sometimes bears the yellow 

 clusters of flowers characteristic of the common laburnum 

 {CylisKS laburniun'), and sometimes purple flowers like those 

 of Cytisus purpurea^ or, again, both these colours may be 

 present in the same flower. I will here quote Darwin's descrip- 

 tion of the plant*: — 'To behold mingled on the same tree 

 tufts of dingy-red, bright yellow, and purple flowers, borne on 

 branches having widely different leaves and manner of growth, 

 is a surprising sight. The same raceme sometimes bears two 

 kinds of flowers, and I have seen a single flower exactly divided 

 into halves, one side being bright yellow and the other purple, 

 so that one half of the standard-petal was yellow and of larger 

 size, and the other half purple and smaller. In another flower 

 the whole corolla was bright yellow, but exactly half the calyx 

 was purple. In another, one of the dingy-red wing-petals had 

 a narrow bright yellow stripe on it ; and lastly, in another 

 flower, one of the stamens, which had become slightly foliaceous, 

 was half yellow and half purple.' 



The result of the struggle of the parental idants evidently 

 cannot depend in the case of Cytisus adami, as it does in that 

 of the individual characters of the human race, upon the fact 

 that the number of homodynamous determinants varies in the 

 parental idioplasm according to the part concerned : for were 

 this the case the same parts of the flowtr could not sometimes 

 be yellow in some instances and red in others, — all the flowers, 

 on the contrary, would display the same composition as regards 

 the parental hereditary parts, even though slight variations might 

 occur, such as would be produced by a dissimilarity in the con- 

 ditions of nutrition. As in the case of the hybrids of Oxalis 

 already mentioned, the flowers would at least display a certain 

 combination of parental characteristics which would be uniform 

 in one and the same plant. The fact that this is not the case, 

 seems to me to aff"ord a decisive proof that Cytisus adami is a 

 real graft-hybrid^ and not an ordinary seminal hybrid^ as in 

 fact was stated to be the case by the nurseryman Adams, who 

 first produced it. I therefore consider the controversy ended 

 as to whether graft-hybrids exist at all, and offer the following 

 explanation of the hereditary phenomena concerned. 



* Loc. cit., Vol. I., p. 414. 



