NAUDIN 159 



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 Kolreuter, 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. 



