350 APPENDIX 



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 

 finallj^ a form is arrived at which is like B and constant in its prog- 

 eny. By this process the species A would change into the species 

 B. Gartner alone has effected thirty such experiments with plants 

 of genera Aquilegiay 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 experiments. 

 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 genera- 

 tions." 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 Pisnm, the entire 

 process of transformation would find a fairly simple explanation. 

 The hybrid forms as many kinds of egg cells as there are constant 

 i' 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 characters which are united by the fertilisation. 

 Let us, for instance, assume that the plants selected for experiment 

 differed in three characters, and the species ABC is to be trans- 

 formed into the other species abc by repeated fertilisation with the 

 pollen of the latter ; the hybrids resulting from the first cross form 

 eight different kinds of egg cells, viz., 



ABC, ABc, AbC, aBC, Abc, aBc, abC, abc. 



/, 



