Systematic and Sexual Relationship. 593 
The simplest form to which it has been proposed to 
reduce the parallel between systematic and sexual rela- 
tionship, is the following: (1) Plants which produce 
offspring when crossed with one another, always belong- 
to the same genus; (2) Plants whose fertility is not 
diminished in crossing belong to the same systematic 
species (or collective species). Both generalizations are 
in great favor and are defended by prominent investi- 
gators. They have, however, a weak side, viz., that they 
cannot be reversed. 
Let us first examine the former proposition. It de- 
nies the existence of hybrids between distinct genera, 
or so-called generic hybrids. It originated amongst those 
philosophers who regarded the genera as having been 
created, the species, however, as having arisen from them 
by natural means. We have already dealt with the his- 
torical significance of these transmutationists in the first 
volume (p. 17). To them the view, stated above, is also 
due, that not only do species arise within the genera by 
a normal process of evolution, but that new forms may 
arise from these species by crossings. W. HERBERT is 
the most famous representative of this view. 1 which was 
later defended by GODRON. The latter investigator de- 
scribes all genera, the species of which are fertile with 
those of related genera as artificial, and has collected a 
mass of evidence in support of this view. 2 
No fundamental objection can be brought against this 
view, and its adoption would lead in relatively few cases 
1 W. HERBERT, Amaryttidaceae, With a Treatise Upon Cross-bred 
Vegetables, London 1837, PP- 337 et sec l- See also GARTNER, loc. cit., 
p. 152, and NAGELI, Sitzungsbcr. d. k. bayr. Akad. d. Wiss., Dec. 15. 
1865, p. 400. 
2 A. GODRON, De I'cs^ecc et des races dans les etres organises, 1859, 
Vol. I, pp. 225-236, and Mem. A cad. Stanislas a Nancy, 1862, pp. 296- 
298. 
