4.16 GRAFT-HYBKIDS. Chap. XL 



whole case has been attributed by some authors to bud-yariation ; 

 but considering the wide difference between C. luhvrnum and 

 pwjmreus, both of which are natural species, and considering the 

 sterility of the intermediate form, this view may be summarily 

 rejected. We shall ])resently see that, with hybrid i^lants, two 

 embryos differing in their characters may be developed within the 

 same seed and cohere ; and it has been supposed that C. adami 

 thus originated. Many botanists maintain that C. adumi is a 

 hybrid produced in the common way by seed, and that it has 

 reverted by Iwds to its two parent-forms. Negative results are not 

 of much value ; but Eeisseck, Caspary, and myself, tried in vain to 

 cross C. Jahunnnn and purjv ir cits ; when I fertilised the former with 

 pollen of the latter, I had the nearest approach to success, for pods 

 were formed, but in sixteen days after the withering of the flowers, 

 they fell off. Nevertheless, the belief that C. udcnni is a spon- 

 taneously produced hybrid between these two species is supported 

 by the fact that such hybrids have arisen in this genus. In a bed 

 of seedlings from C. elongatus, which grew near to C. purpureus, and 

 was probably fertilised by it through the agency of insects (for 

 these, as I know by experiment, play an important part in the fer- 

 tilisation of the laburnum), the sterile hybrid C. purpureo-elongatus 

 appeared.'-"^ Thus, also, Waterer's laburnum, the C. al/n'nc-htb'ir- 

 7ium^'' spontaneously appeared, as I am informed by ]\Ii'. Waterer, 

 in a bed of seedlings. 



On the other hand, we have a clear and distinct account given to 

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

 is not an ordinary hybrid; but is wliat 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 mannei- a shield of the 

 bark of C. purpureus into a stock of C. lalmnnnn ; 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. purjnireus, and 



^^ Braun, in ' Hot. Mem. Eay. Soc.,' from "--:th parent-species, during some 



1853, p. xxiii. seasons yielded no good seeds ; but in 



^' This hybrid has never been de- 18(36 it was unusually fertile, and its 



scribed. It is exactly intermediate in long racemes produced from one to 



foliage, time of flowering, dark stria; occasionally even four pods. Many 



at the base of the standard petal, of the pods contained no good seeds, 



hairiness of the ovarium, and in but generally they contained a single 



almost every other character, be- apparently good seed, sometimes two, 



tween C. la'mrnum and alpinus ; but and in one case three seeds. Some of 



it approaches the former species more these seeds germinated, and I raised 



nearly in colour, and exceeds it in two trees from them ; one resembles 



the length, of the racemes. We have the present form; the other has a 



before seeJ that 20-3 per cent, of its remarkable dwarf character with 



pollen-grains are ill-formed and small leaves, but has not yet flowered, 



worthless. My plant, though grow- *' ' Annales de la Soc. de I'Hort. de 



mg not above thirty or forty yards Paris,' tom. vii., 1S30, p. 93. 



