in Hybridisation 375 



in an entirely free and equal arrangement, by 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 scope. 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 

 and grouping of the elements which exist in the foundation- 

 cells [fertilised ova] of the same in vital interaction*. 



Even the validity of the law formulated for Pisum 

 requires still to be confirmed, and a repetition of the more 

 important experiments is consequently much to be desired, 

 that, for instance, relating to the composition of the hybrid 

 fertilising cells. A differential [element] may easily escape 

 the single observer^, which although at the outset may 

 appear to be unimportant, may yet accumulate to such 

 an extent that it must not be ignored in the total result. 

 Whether the variable hybrids of other plant species observe 

 an entire agreement must also be first decided experiment- 

 ally. In the meantime we may assume that in material 

 points an essential difference can scarcely occur, since the 

 unity in the developmental plan of organic life is beyond 

 question. 



In conclusion, the experiments carried out by Kolreuter, 

 Gartner, and others with respect to the transformation of 

 one species into another by artificial fertilisation merit 

 special mention. Particular importance has been attached 



* " Welche in den Grundzellen derselben in lebendiger Wechselwirkung 



stehen." 



t "Dem emzelnen Beobachter kann leicht etn Differ enziale entgehen" 



