358 Menders Experiments 



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 

 its progeny. By this process the species A would change 

 into the species B. Gartner alone has effected thirty such 

 experiments with plants of genera Aquilegia, Dianthus, 

 Geum, Lavatera, Lychnis, Malva, Nicotiana, and Oenothera. 

 The period of transformation was not alike for all species. 

 While with some a triple fertilisation sufficed, with others 

 this had to be repeated five or six times, and even in the 

 same species fluctuations were observed in various experi- 

 ments. Gartner ascribes this difference to the circumstance 

 that "the specific \typische\ power by which a species, during 

 reproduction, effects the change and transformation of the 

 maternal type varies considerably in different plants, and 

 that, consequently, the periods within which the one species 

 is changed into the other must also vary, as also the number 

 of generations, so that the transformation in some species 

 is perfected in more, and in others in fewer generations." 

 Further, the same observer remarks "that in these trans- 

 formation experiments a good deal depends upon which type 

 and which individual be chosen for further transformation." 



If it may be assumed that in these experiments the 

 constitution of the forms resulted in a similar way to that of 

 Pisum, the entire process of transformation would find a 

 fairly simple explanation. The hybrid forms as many kinds 

 of egg cells as there are constant combinations possible 

 of the characters conjoined therein, and one of these is 

 always of the same kind as that of the fertilising pollen 

 cells. Consequently there always exists the possibility with 

 all such experiments that even from the second fertilisation 

 there may result a constant form identical with that of the 

 pollen parent. Whether this really be obtained depends in 

 each separate case upon the number of the experimental 

 plants, as well as upon the number of differentiating 



