148 PLANT HYBRIDIZATION BEFORE MENDEL 



the majority of the descendants, in his experiments, resembled 

 their immediate parent, and that the power of that which he calls 

 "direct heredity" is altogether preponderant. From the fact that 

 now and again a plant would "take back" to a more remote an- 

 cestor, he concluded that "atavism" was also a constant and ten- 

 acious force to be reckoned with. 



"It is this force," he observes, "which causes to reappear the characters 

 of the great mass of the ancestors among distant descendants, across 

 numerous generations presenting different characters. The action of this 

 force may appear limited, if one considers only its influence upon a 

 single generation, but, if one reflects that it acts constantly and always 

 in the same direction, it is explained that it suffices to maintain the 

 fixity of plant species." (7b, p. 10.) 



Elsewhere, Vilmorin further remarks regarding the forces in- 

 volved in inheritance : 



"We come first, for the greater simplicity, to consider atavism as con- 

 stituting a single force, but, if one reflects, one will see that it presents 

 rather a bundle of forces acting almost in the same direction, and com- 

 posed of the individual call or attraction of all the ancestors. Now, to 

 facilitate the intelligence of action of this force, it will be necessary 

 for us to consider first, and in an abstract manner, the force of the re- 

 semblance to the mass of the ancestors, which may be considered as 

 due to the attraction of the type of the species, and to which we shall 

 reserve the name of atavism; then separately, and in a more special man- 

 ner the attraction of the force of resemblance to the father direct, or 

 heredity, which, less powerful but nearer, will tend to perpetuate in the 

 child the characters proper to the immediate parent." 



Another conclusion which Vilmorin draws, is as to 



". . . the very rapid enfeebling of the influence of heredity beyond 

 the first generation, in other terms, the little tendency which plants 

 show to resemble any ancestor exhibiting characters other than those 

 of the mass of ancestors, if this ancestor is not the immediate author of 

 the plants. We have seen frequent examples of blue plants issued from 

 two or three generations of rose plants, and giving birth nevertheless 

 to a progeny entirel}' or almost blue." 



As to the conclusion which one may draw from these experi- 

 ments, he says : 



"It will not be a mathematical evaluation of the comparative power 

 of the different forces which act upon the transmission of the characters 

 in the plants. On the other hand, in a word, one knows that the phe- 

 nomena in which the vital forces intervene do not permit themselves 

 to be reduced to figures, and on the other hand, were it otherwise, that 

 the number of individuals observed in each generation would not be 

 enough to give precise numbers, limited as that was by that of the seeds 

 of the hybrid plants, the seeds being in Lupinus hirsutus very large and 

 few." 



