A GRAIN OF WHEAT 43 



a race Y by three characters, i. e., by the gens A B C (for example, 

 A = long head; 5 = awned glumes; (7 = rust resistance), to which 

 the race Y opposes ab c. These are antagonistic characters (a = short 

 head; & = awnless glumes; c = capacity for rust infection). A is the 

 antagonist of a, B of &, etc. But A is not antagonistic to 6 or c, nor 

 B to a and c. 



As long as the plant is self-fertilized, the mosaic of its characters is 

 maintained. But if it is fertilized by a distinct race several cases can 

 arise in the course of successive generations. The product called a 

 hybrid (Fj^ films 1) is evidently the sum of the two parents 

 (X -J- Y) ; if forms not closely related to each other are crossed, the 

 hybrid generally takes a form intermediate between the two parents. 

 We shall not speak of these hybrids here, for they are generally sterile 

 and practically useless for cereal culture. If, on the other hand, 

 closely related forms are fused in the hybrid (F x ) the characters of the 

 father or the mother exclude those of the other parent; one of the 

 parents seems to have been absorbed by the other. Then we say that 

 the character of the father or of the mother dominates or vice versa. 

 Let us take two parents X and Y, differing in the antagonistic char- 

 acters A B C for X and a b c for Y. The hybrid (F 1 = X + Y) will 

 have the appearance A, B, C, if the total gens of X dominate those of 

 Y, or the appearance a, &, c in the contrary case. In other words, one 

 of the parents may seem to be absorbed by the other. But it often 

 happens that if A dominates a, & dominates B, c dominates (7. 



But if this hybrid (F x ) is allowed to fertilize itself, its direct 

 descendants, i. e., the second generation (F 2 ), show that the character 

 or characters which had disappeared reappear in a proportion which 

 can be predicted with almost mathematical certainty. I can not take 

 the time to explain to you the details of this phenomenon. But the 

 most astonishing thing is that among the descendants of the second 

 generation (F 2 ) (that is, the descendants of the hybrid by self-fertiliza- 

 tion) there are (1) those resembling the father exclusively (X), or 

 the mother (Y) ; (2) new forms, *. e., those in which a part of the 

 paternal and maternal characters are combined in a new mosaic. 



To choose a very simple example, if the two parents differed by 

 their two pairs of characters A B and a 1}, the hybrid of the first gen- 

 eration (F x ) would bear the apparent characters A B or a ~b, that is, 

 it would resemble the father or the mother exclusively, according to 

 the predominance; that of the generation (F 2 ) would comprise indi- 

 viduals of different sorts: AB, Ah, Ba, db. The two combinations Ab 

 and Ba are new. 



If, in a second case, the antagonistic gens are ABC for (X) and 

 a & c for (Y), the first generation might be A B C, but in the second 



