in Hybridisation 89 



vessels and anthers are of one kind, and agree with the 

 fundamental compound cell [fertilised ovum]. 



With regard to those hybrids whose progeny is variable 

 we may perhaps assume that between the differentiating 

 elements of the egg and pollen cells there also occurs a 

 compromise, in so far that the formation of a cell as 

 foundation of the hybrid becomes possible; but, never- 

 theless, the arrangement between the conflicting elements 

 is only temporary and does not endure throughout the life 

 of the hybrid plant. Since in the habit of the plant no 

 changes are perceptible during the whole period of vege- 

 tation, we must further assume that it is only possible for 

 the differentiating elements to liberate themselves from the 

 enforced union when the fertilising cells are developed. In 

 the formation of these cells all existing elements participate 

 in an entirely free and equal arrangement, in which it 

 is only the differentiating ones which mutually separate 

 themselves. In this way the production would be rendered 

 possible of as many sorts of egg and pollen cells as there 

 are combinations possible of the formative elements. 



The attribution attempted here of the essential difference 

 in the development of hybrids to a permanent or temporary 

 union of the differing cell elements can, of course, only 

 claim the value of an hypothesis for which the lack of 

 definite data offers a wide field. Some justification of the 

 opinion expressed lies in the evidence afforded by Pisum 

 that the behaviour of each pair of differentiating characters 

 in hybrid union is independent of the other differences 

 between the two original plants, and, further, that the 

 hybrid produces just so many kinds of egg and pollen 

 cells as there are possible constant combination forms. 

 The differentiating characters of two plants can finally, 

 however, only depend upon differences in the composition 



