024 



THE AMERICAN NATURALIS1 



[Vol. XLIX 



ceding generation (see Fig. 1) ; the following diagram 

 shows the mode of inheritance in such races : 



Miss Saunders (1911 ; 1913 ; Bateson, 1909 T pp. 201-204) 

 has done a great amount of work on heredity in Matthiola, 

 and has developed an ingenious hypothesis to explain the 

 peculiar behavior of doubleness. Goldschmidt (1913) has 

 given another explanation, which has been vigorously 

 criticized by Miss Saunders. Several years ago (per- 

 haps in 1909), largely on the basis of Miss Saunders's evi- 

 dence, I formulated a hypothesis somewhat simpler than 

 either of those just mentioned. 



In view of the special interest of the case at present, 

 and the fact that one or both of the essential points of 

 my explanation have been suggested incidentally by an- 

 other writer (Belling, 1915, 1915a), it seems desirable to 

 give a general review of the hypotheses at this time. 2 



As Miss Saunders's (1911; Bateson, 1909, p. 201-204) 

 crosses have shown, the "double-throwing" singles are 

 heterozygous, the approximately 1 :1 ratio being due to 

 the fact that the functional pollen is all double-carrying. 

 This is shown by ^\lis> Saunders's crosses between double- 

 throwers and pure singles. When the double-thrower 

 is the seed-parent, about half the F, progeny are hetero- 

 zygous, the rest being pure singles ; about half the double- 

 thrower eggs, then, are ' 1 double-carrying. ' ' On the other 



Single 



Single 



Double 

 (sterile) 



Single 



