270 DR J. M. MACFARLANE ON THE 



those of Hansen * on adventitious bud formation from previously permanent tissue, the 

 above hypothesis is worthy of careful consideration, and it may even be that the contact 

 of the two sets of cells of stock and graft causes a physiological stimulus analogous to 

 that of fertilisation. But in all the experiments on graft hybridisation summarised by 

 Darwin t the strong balance of evidence is in favour of fusion of half buds, except 

 perhaps with Poynter's Rose, where a nearer approach to an ordinary seminal hybrid 

 rather than to a composite plant, such as C. Adami, was obtained by what appears from 

 description like adventitious bud formation. 



For the following reasons, then, we would regard C. Adami as a graft hybrid of 

 pronounced type : — (1) Adam's account of its origin is perfectly natural ; (2) experiments 

 on potatoes and hyacinths have in several cases produced organisms quite comparable to 

 C. Adami; (3) while a few seed hybrids, such as Noble's Clematis and Berberis Neuberti, 

 show an inclination to reversion in some of their parts to the parent type, we have none 

 which present the pure parents growing side by side with the hybrid as an organism ; 

 (4) the production of good and abundant seeds by the pure parts of the composite 

 organism which yield offspring like those parts, is totally different from anything that we 

 know of seed hybrids, though these do at times give rise to offspring some of which 

 resemble one parent pretty strongly and some the other ; (5) that the segregation of 

 mixed characters along with blending to an intermediate degree of others is unlike what 

 we usually find in seed hybrids, though some of these show a tendency at times in this 

 direction. 



In that case, we must admit, as pretty surely established, that cell unions may be 

 effected without intervention of sexual elements, and that such unions can give rise to an 

 organism, the flowers of which are not materially different from those of a sexual hybrid. 



V. General Summary of Results on Seed Hybrids. 



We may now briefly recapitulate some of the more evident or naked-eye characters of 

 hybrids, and gradually pass to finer details. It has been demonstrated that in hair 

 production, if the parents possess one or more kinds that are fundamentally similar, but 

 which differ in size, number, and position, the hybrid reproduces these in an intermediate 

 way. Illustrations of this were presented by Geum intermedium, Erica Watsoni, 

 Cypripedium Leeanum, and Masdevallia Chelsoni. But if only one parent possess hairs 

 over a given region the hybrid usually inherits these to half the extent, as in the petals 

 of Dianthus barbatus and some floral parts of Bryanthus erectus. If the hairs of two 

 parents are pretty dissimilar, instead of blending of these in one, the hybrid reproduces 

 each, though reduced in size and number by half. The gland hairs of Saxifraga 

 Andreivsii, the simple and gland hairs of Ribes Culverwellii, and those on the vegetative 

 organs of Bryanthus erectus are examples. The peculiar case of hair distribution in 



* Abhand. d. Senckenb. nut. Geseli, Bd. xii. 



f- Animals and Plants under Domestication, 2nd edit., vol. i. pp. 419-422. 



