90 Mendel's Experiments 



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 a difference in principle 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 tlie transformation of 

 one species into another by artificial fertilisation merit 

 special mention. A special importance has been attached 

 to these experiments, and Gartner reckons them among 

 "the most difficult of all in hybridisation." 



If a species A is to be transformed into a species B, 

 both must be united by fertilisation and the resulting 

 hybrids then be fertilised with the pollen of B\ then, out 

 of the various offspring resulting, that form would be 

 selected which stood in nearest relation to B and once 

 more be fertilised with B pollen, and so continuously until 

 finally a form is arrived at which is like B and constant in 



* " Welche in den Grundzellen derselben in lebendiger Wechsel- 

 wirkunf) stehen." 



t "Dem einzelnen Beobachter kann leicht ein Differenziale ent- 

 gehen." 



