46 PLANT HYBRIDIZATION BEFORE MENDEL 



"Experience teaches us," he says, "that from the union of two like- 

 formed fluid fertilizing materials of different sorts a firm and organic 

 body originates, and that every natural plant itself provides those two- 

 fertilizing materials required for a new procreation, and especially the 

 one of them, namely, the male, apparently in much larger measure than 

 was necessary for its reproduction." {ib., p. 44.) 



On the other hand, according to Kolreuter's view, an artificial 

 process seems to be quite impotent for fertilization purposes, or 

 else it brings it about only in a very limited and incomplete way. 

 This circumstance he holds to be one of the most complicated 

 knots in the whole doctrine of reproduction, 



"to the solution of which all human understanding taken together might 

 still perhaps be too weak." He concludes that: "I will hence not in the 

 least break my head on it, but simply lay it down as a fundamental ex- 

 perience when, later on, the question arises of the explanation of various 

 remarkable characters of a few of the plants obtained from my experi- 

 ments." (p. 45.) 



Thus concludes the theoretical or introductory portion of the 

 "Fortsetzung." Of the experiments which follow, 18 are with 

 species of Nicotiana^ one with Dianthus, one with Ketmia^ one with 

 Leucojum^ and one with Hyoscyamus. 



Of the Nicotiana crosses, five are too complicated to be of 

 genetic value, consisting either of crosses of one F^ hybrid with 

 a different one, or of an F^^ with a cross between a species and 

 another F-^. Nine of the crosses might be considered interesting 

 from the genetic standpoint, being either crosses between species, 

 selfing of F^'s or back crosses on an F^^ by one of the parents and 

 vice versa. 



Kolreuter made, besides other crosses between species of Nico- 

 tiana^ crosses between species of Ketmia^ pink {Dianthus)^ stocks 

 (Matthiola), dogbane (Hyoscyamus) , and mullein (Verbascum). 

 He ascertained the fact that, in general, only nearly related 

 plants, and not always even these, can be crossed. He determined 

 experimentally the fact that, if the stigmas of flowers are polli- 

 nated at the same time by their own pollen and by pollen from 

 another species, fertilization is effected by the former, which 

 would account for the comparative rarity of "species hybrids" in 

 nature. 



The cross Nicotiana rustica X paniculata was repeated, 24 

 plants resulting, which resembled in behavior those of the first 



