PLANT HYBRIDIZATION BEFORE MENDEL 193 



they are united to form intermediate characters, which are only incom- 

 pletely accommodated." 



Farther on (p. 263), he comments on the fact that two hybrid- 

 izing forms, because they furnish each a single fertilizing cell, 

 share, equally in the hybrid product. It is not assumed, he says, 

 that two different plants have their reproductive cells qualita- 

 tively and quantitatively similarly fitted out, but it may be as- 

 sumed on the contrary, that the reproductive cells of different 

 species, varieties, and individuals, are always dissimilarly consti- 

 tuted, and that hence that plant which forms the active material 

 in greatest quantity and of best quality has always the preponder- 

 ance in the fertilization. 



The discussion of the nature of the hybrid in "Die Theorie der 

 Bastardbildung" (4e) is further to be summarized as follows : 



Two species of different genera, or of different sections of the 

 same genus, do not ordinarily bring about cell division in the 

 embryo, the fertilization remaining without result. If the hybrid-^ 

 izing forms are a little more nearly related, the embryo remains 

 few-celled and dies out. With nearer relationship, the embryo de- 

 velops but does not germinate ; or it germinates, but forms a very 

 weakly plant which soon dies, or else a weakly plant which flowers 

 but does not bear seed. As the relationship of the parental forms 

 becomes closer, the vitality of the hybrid increases, reaching its 

 maximum as a rule, when nearly related varieties mutually cross. 

 He concludes that the unlike viability of the product proceeding 

 from self-fertilization, in-breeding, crossing of varieties, and the 

 hybridization of species, respectively, is due to the greater or 

 lesser degree of disturbances taking place in the individual, and 

 the general initial adaptability of the fertilizing cells. Since vege- 

 tative growth and reproduction are two essentially different func- 

 tions, two types of mutual adaptation must be assumed, the vege- 

 tative and the sexual. Neither of these is complete, inasmuch as 

 the one partly excludes the other. The sexual harmony (Concor- 

 danz) is much more easily disturbed than the vegetative. Hence, 

 under deleterious influences, a plant usually limits, first its seed 

 reproduction, and long afterward its vegetative activity. The in- 

 fertility of a hybrid depends upon the disturbance of the sexual 

 adaptation, i.e., upon whether the pollen tube of the one and the 

 germinal vesicle of the other form a union capable of develop- 



