178 REPORT— 1891. 



of Weismann's essay on heredity is the following comment on 

 the case of Begonia : " But I think that this fact only proves 

 that in Begonia and similar plants all the cells of the leaves, 

 or perhaps only certain cells, contain a small amount of germ- 

 plasm, and that, consequently, these plants are specially 

 adapted for propagation by leaves." In other v^^ords, Weis- 

 mann here, without seeming to be at all conscious of it, 

 abandons the dogma of the isolation of the germ-plasma. For 

 the case of Begonia is by no means an isolated one ; and there 

 is abundance of evidence that this diffusion of the germinal 

 matter through the differentiated cells is quite general in the 

 vegetable kingdom, and is by no means rare in animals. 



Still more cogent is the evidence afforded by the phenomena 

 of graft-hybrids, phenomena the great significance of which 

 was recognised and insisted upon by Darwin, though they seem 

 to have been entirely overlooked by Weismann. In "The 

 Variation of Animals and Plants under Domestication," 

 Darwin brings together all the cases at that time known. 

 One of these is Adam's Laburnum, which is a form inter- 

 mediate between Cytisus lahiirnuvi and C. lyurinireus. To 

 quote Darwin's words, " Throughout Europe, in different soils 

 and under different climates, branches on this tree have re- 

 peatedly and suddenly reverted to the two parent species in 

 their flowers and leaves. To behold mixed upon the same tree 

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

 branches having widely-diiferent leaves and manner of growth, 

 is a surprising sight. . . . The most remarkable fact 

 about this tree is that in its intermediate state, even when 

 growing near both parent species, it is quite sterile, but when 

 the flowers become pure yellow or pure purple they yield 

 seeds. . . . We have a clear and distinct account given to 

 Poiteau by M. Adam, who raised the plant, showing that C. 

 adami is not an ordinary hybrid, but is what may be called a 

 graft-hybrid — that is, one produced from the united cellular 

 tissue of two distinct species. M. Adam inserted in the usual 

 manner a shield of the bark of G. purpureus into a stock of 

 G. lahurnum ; and the bud lay dormant, as often happens, for 

 a year ; the shield then produced many buds and shoots, one 

 of which grew more upright and vigorous with larger leaves 

 than the shoots of C. j^n-J'jyureus, and was consequently pro- 

 pagated." 



Other cases, the particulars of which are given by Darwin, 

 are those of the Bizzarria orange, which is a graft-hybrid 

 between the bitter orange and the citron ; graft-hybrids 

 between light- and dark-fruited vines, between bulbs of different 

 kinds of hyacinths, and between different kinds of potatoes — 

 new varieties being produced in this last case by grafting 

 together portions of the tubers of two quite distinct kinds. 



