LN THE TROPICS. 
usually more fertile than those between different species ; 
and that hybrid plants often excel their parents in luxuriance 
of growth. Kolreuter attached importance to the number 
of generations in which by continually fertilizing the suc¬ 
cessive offspring of a hybrid with the pollen of one parent, 
plants exactly resembling this parent could be obtained. 
These latter facts were subsequently discussed by Mendel 
and explained by him in terms of his own theory. 
T. A. Knight was the earliest observer to lay stress upon 
the practical side of the study of hybrids, and he was largely 
concerned with the improvement of useful races of plants 
by cross-breeding. The account of his experiments with peas 
(44) was published in 1779. The agreement of the facts 
then described with those of Mendel has been pointed out 
by Bateson (2). 
Between 1800 and 1860 a large number of workers were 
concerned with the raising of hybrids, but there was no 
great advance in theoretical knowledge. Gaertner, in 1849, 
published an enormous mass of observations largely confirm¬ 
ing and amplifying those of Kolreuter. 
C. Naudin’s essay entitled “ New Researches on Hybridity 
in Plants ” appeared in 1862 (52). He pointed out that the 
facts of the return of hybrids to the specific forms of their 
parents, already observed by Kolreuter and Gaertner, were 
naturally explained by the hypothesis of the disjunction of 
the two specific essences in the pollen and ovules of the 
hybrid. In cases where this is complete, forms exactly 
resembling the parents might be obtained. This hypothesis 
comes remarkably near to that of Mendel ; and the import¬ 
ance of the uniformity of the first hybrid generation, as 
contrasted with the diversity of the second, is clearly recog¬ 
nized. Naudin considered the hybrid in the adult Btate to 
consist of an aggregate of particles, homogeneous and charac¬ 
teristic of a single species when taken separately, but 
mingled in various proportions in the organs of the hybrid 
plant, which is thus looked upon as a “ living mosaic.” 
