PLANT HYBRIDIZATION BEFORE MENDEL 327 



De Vries : 



Das Spaltungsgesetz der Bastarde. 



Ber. d. d. bot. Ges., VoL 18, pp. 83-90. (la). 

 In this communication, De Vries again cites his Intracellular 

 Pangenesis (pp. 60-75) ^^^ ^^^ original thesis, that: 



"The whole character of the plant is built up of definite units. These 

 so-called elements of the species, or elementary characters, one thinks of 

 as bound to material carriers. To each individual character there corre- 

 sponds a special form of material carrier. Transitions between these ele- 

 ments are as little found as between the molecules of chemistry." (la, 

 p. 83.) 



De Vries then goes on to say : 



"In this latter domain [i.e., that of hybrids], it demands a complete 

 changing about of the views from which investigation has to proceed. 



"Nowhere as clearly as here [i.e., in the experiments on crossing and 

 hybridization] does the image of the species appear in contra-distinction 

 to its composition out of independent factors in the background." (Intra- 

 cellular Pangenesis, German ed., 1889, p. 25.) 



De Vries then comments on the fact that the tlien existing 

 doctrine regarding hybrids regards species, sub-species, and vari- 

 eties, as the units, the combination of which form hybrids, a 

 distinction being made between crosses of varieties, and the true 

 hybrids of species, (la, p. 84.) 



This attitude is, according to his views, to be given up for 

 physiological investigation, (la, p. 84.) 



"in its stead is to be placed the principle of the crossing of species- 

 characters. The units of species-characters are accordingly to be re- 

 garded and studied as sharply separated magnitudes. They are to be 

 treated as being independent of one another everywhere, and as long 

 as no grounds for the contrary are apparent. In every crossing experi- 

 ment, there is accordingly only one character, or a definite number of 

 such, to be taken into observation : the remainder may, for the time, be 

 left out of consideration. Or rather it is indifferent whether the parents 

 differ from one another in still other points. For the experiments, how- 

 ever, manifestly the hybrids, both of whose parents differ only in the 

 one character, form the simplest cases [monohybrids in contrast to di- and 

 polyhybrids]." 



If the parents of a hybrid diverge from one another in only 

 one point, or If one takes one or a few of their points of differ- 

 ence Into consideration, then they are In these characters an- 

 tagonistic. In all others alike, or, for the calculation. Indifferent ; 

 the crossing experiment will therefore be limited to the antagonis- 

 tic characters. 



