GRAFT-HYBRIDS. 573 



poulterers in Innsbruck receive for sale on an average six specimens every year 

 from huntsmen in the immediate neighbourhood. The plumage of some individual 

 examples of Tetrao medius is curiously striped with alternate groups of feathers 

 inherited from T. tetrix and T. Urogallus respectively. In 1879 a huntsman brought 

 me from the remotest part of the Gschnitzthal in Tyrol a hen of Tetrao Tnedius 

 whose plumage exhibited a mixture of the feathers of T. tetrix and T. Urogallus, 

 irregularly distributed in stripes and patches all over the body. The case of this 

 hybrid affords valuable confirmation of the results of the experiments made on 

 Iris hybrids, and there can no longer be any doubt of the fact that there are hybrids 

 generated by crossing in which the parental characters reappear in juxtaposition. 



In spite of all this, however, I should not like to deny the possibility of the 

 existence of graft-hybrids, for there are certain considerations which tend to a con- 

 trary conclusion. In most cases the relation to the substratum of those cells of the 

 ingrafted shoot or bud which take the crude nutrient sap from the stem of the 

 stock-plant is just the same as that of a parasite's suckers; they are clearly marked 

 off from the cells of the substratum and are not influenced thereby either in their 

 shape or in their ultimate structure, whilst, conversely, no essential modification is 

 undergone by the substratum through the presence of the graft. There is nothing, 

 however, to exclude the possibility of a fusion between the protoplasmic contents of 

 adjacent cells taking place at the spot where stock and graft unite, and the con- 

 sequent development of a tissue which is composed of cells arising from a division 

 of the cells containing the mixed protoplasms, and which unites the characteristic 

 features of the tissues belonging to the stock and to the graft respectively. In fact, 

 something of the kind has been observed in the case of the parasitic Balanophoreae 

 (see vol. i. p. 194). Now supposing such an intermediate tissue were to be formed 

 at the junction between a graft and its substratum, one or more shoots might spring 

 from it and they would doubtless combine the characteristics of the two species 

 employed as stock and scion. 



In relation to the genesis of new forms of plants in nature, the question of the 

 possibility of the existence of graft-hybrids is of secondary importance ; but it is of 

 no small moment in connection with the comprehension of the processes involved in 

 hybridization; for, the researches suggested by this problem have led to the con- 

 clusion that the marks and attributes of a particular species which are percep- 

 tible to our senses are an outward sign corresponding to the ultimate structure 

 and molecular composition of a specific protoplasm, and that wherever the special 

 characters of two species are united in a single plant-form, that form is built up 

 from protoplasm which owes its origin to a combination of the protoplasms of two 

 parent-species. 



It is only by adhering to this train of thought that one is able to understand 

 how it is that, also in the matter of chronological development, the vital manifesta- 

 tion connected with the shape, anatomical structure, scent, and colour occupy in 

 hybrids a position intermediate between the corresponding manifestations in the 

 parental species. In the Botanic Garden at Vienna there has been for many years 



