170 THE OLDER HYBRIDISTS 
constantly sterile, and this led him to the further 
conclusion, now believed to be erroneous, that the 
separate genera or families were those which were 
originally created, whilst he believed that the separate 
species of the same genus arose from a single original 
type by a genuine process of evolution. 
The most prolific in work of all the hybridists, how- 
ever, was undoubtedly Carl Friedrich v. Gaertner 
(1772-1850). Gaertner made a great number of 
crosses between species belonging to all sections of 
the natural system, and his book, published in 1849, 
contains a great mass of valuable information. Gaert- 
ner’s theoretical conclusions, for the most part, only 
amplify and confirm those of Koélreuter, upon whom 
in this direction he made but little advance. 
C. Naudin’s essay, entitled ‘New Researches on 
Hybridity in Plants,’ made its appearance in 1862. 
The author pointed out that the facts of the return 
of hybrids to the specific forms of their parents, when 
repeatedly crossed with the latter, are naturally ex- 
plained by the hypothesis of the disjunction of the 
two specific essences in the pollen grains and ovules 
of the hybrid. The idea may, perhaps, be made some- 
what clearer as follows : Let us consider the case of a 
species A crossed with another species B. Naudin 
supposes that some of the pollen grains and ovules of 
the hybrid plant will be potentially* of the exact 
* When it is said that a pollen grain or ovule potentially 
resembles the species A, it is meant that the germ-cell in 
question is of such a kind that, when united with one derived 
from an ovule or pollen grain of similar constitution, it would 
give rise to a plant exactly resembling A. 
