CYTISDS ADAMI. 445 



variegated forms of Abutilon have been grafted on green-leaved 

 stocks, they have been known to affect many of the subsequent 

 shoots. Such cases are known as graft-hybrids. The most 

 remarkable example is that of Cytisus Adami, a form midway 

 between Cytisus laburnum and purpureus. Of this plant Darwin 

 says : " Throughout Europe, in different soils and under different 

 climates, branches on this tree have repeatedly and suddenly re- 

 verted to both parent species in their flowers and leaves. " To 

 behold mingled on the same tree tufts of dingy red, bright yel- 

 low, and purple flowers, borne on branches having widely differ- 

 ent 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 in 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 an- 

 other, one of the dingy-red wing-petals had a bright yellow 

 narrow stripe on it ; and lastly, in another flower one of the 

 stamens, which had become slightly foliaceous, was half yellow 

 and half purple ; so that the tendency to segregation of char- 

 acter or reversion affects even single parts and organs. The 

 most remarkable fact about this tree is that in its intermediate 

 state, even when growing near both its parent species, it is 

 quite sterile ; but when the flowers become pure yellow or pure 

 purple they yield seed." Passing over the views expressed 

 by many that Cytisus Adami is a hybrid produced by seed, the 

 account of its origin, quoted by Darwin, is here given. M. 

 Adam inserted a shield of Cytisus laburnum in the stem of C. 

 purpureus ; the bud lay dormant a year and then produced a 

 shoot which was rather more vigorous than those of C. purpureus ; 

 this shoot was propagated and the plants therefrom were sold as a 

 variety of Cytisus purpureus, before they had come into flower. 1 



1 The account of the budding was published after they had flowered, but 

 before this extraordinary tendency to reversion had been manifested. Upon 

 a review of the testimony Darwin was inclined to accept the foregoing account 

 of the origin of Cytisus Adami as a graft-hybrid as true. Other cases are to 

 be placed in the same category. 



For a full statement of bud-variations and graft-hybrids the student 

 should read: Darwin, Variation in Animals and Plants under Domestication, 

 1868, vol. 1, chap. xi. ; also Focke, Die Pflanzen-mischlinge, 1881, p. 519. 

 In the latter is an interesting account of the mixed oranges (Bizarria). Con- 

 suit also Braun, On the Phenomenon of Rejuvenescence in Nature (Kay Society, 

 1853) ; and numerous papers by Caspary. 



