PLANT HYBRIDIZATION BEFORE MENDEL 239 



from the other would necessarily lead to complete reversion of charac- 

 ter; and it is perhaps not too bold a supposition that unmodified and 

 undeteriorated gemmules of the same nature would be especially apt to 

 combine." (ic, 2:383.) (Italics inserted.) 



This statement approximates toward an explanation of what is 

 understood to occur when two F^ hybrids are mated. The re- 

 union of, say, character-unit or determiner D from the male with 

 D from the female gives DD, which reconstitutes one of the 

 original parents with respect to a character which breeds true; 

 and this is what we now understand "reversion" to be — the res- 

 toration in stable form of characters disunited and scattered or 

 "segregated" 'n the offspring of a cross. 



Continuing, Darwin says : 



"Pure gemmules in combination with hybridized gemmules would lead 

 to partial reversion. And lastly, hybridized gemmules derived from both 

 parent-hybrids would simply reproduce the original hybrid form. All 

 these cases and degrees of reversion incessantly occur, ic, 2:383.) (Italics 

 inserted.) 



The above is an attempt at a statement of the conditions of 

 things in the heterozygous or hybrid condition except that "hy- 

 brid gemmules," or their equivalents, are not believed to exist as 

 such, and the crossing of the F^ with itself yields, of course, not 

 all "hybrids" as Darwin supposed, but leaves only one-half the 

 offspring in the hybrid condition. In the simple Mendelian hybrid 

 it has been found, to be sure, that, in addition to the parental 

 character-types being reproduced pure — i.e., 25 per cent of each — 

 one-half, or 50 per cent, of the individuals in the second genera- 

 tion reproduce again the hybrid form, owing to the factors not 

 being united with their like, but with, as it were, unlike factors, 

 or as it may be the absence of the factor in the opposite parent. 

 However, there are often modifying factors which do come in 

 from the other parent; at all events, the result is oftentimes a 

 dilution of the original character. Assuming the "hybridized" 

 gemmules to represent the "Dr" condition, we have in Darwin's 

 statement what is an approximation towards genetic language. In 

 other words, Darwin's theoretical statement comes rather close to 

 representing the Mendelian point of view in regard to the mating 

 of hybrid organisms of the F^ generation. 



It seems strange indeed that with Darwin's instinct for detail, 

 and the acuteness and accuracy of his sense of observation, it 

 did not occur to him to studv the nature of hvbrids in the same 



