Duplicate genes for capsule-form in Bursa bursa-pastoris. 141 



limited number of seeds produced by each individual. The fact that 

 one of the two fully demonstrated duplicate determiners for the ligula 

 in oats was associated with a particular form of panicle may mean that 

 the two duplicate genes were brought to light by independent mutations 

 resulting in the loss of the ligula-gene from two different chromosomes 

 which had other differences which affected the form of the inflorescence. 

 It must not be inferred, however, that because a character is primitive, 

 it is necessarily, or even generally, represented by duplicate determiners 

 in the germ-cells. The ligula in maize serves to strongly impress this 

 statement, for EMERSON (1912) finds that in each of several independent 

 stocks of maize there is only one pair of genes present for the ligula. 



The very complexity of the capsule- character of Bursa, is, to my 

 mind, against the origin of its duplicate determiners by independent 

 mutations, for not only are there differences in form, size and pigmen- 

 tation, but the entire structural mechanism which provides for the 

 freeing of the mature seeds by the falling off of the valve, including 

 a thickening of the interior epidermis and a definite articulation at the 

 margin of the dissepiment, remain together as a single characteristic or 

 unit-character, whether produced by either of the duplicate genes, C or D, 

 or by both. In my most recent crop of Bursa there were several individuals 

 which showed some modifications of the Heegeri capsule - character, of 

 such a nature as to suggest that the bursa-pastoris capsule -character 

 may be in reality produced by a coupled system of determiners instead 

 of a single determiner. This matter is not yet ready for report but it 

 is under investigation. It is mentioned here only because of the im- 

 portant bearing such coupling of characters would have upon the problem 

 of the method by which the duplication of determiners for the triangular 

 capsule may have been brought about. If the triangular capsule should 

 be found to represent a complex coupled system of determiners acting 

 together as a single unit, the possibility of its duplication by indepen- 

 dent mutations or by longitudinal "crossing-over" between adjacent 

 chromosomes would be nearly incomprehensible. 



It may be possible to get some further experimental evidence that 

 duplication of the capsule-character in Bursa is a comparatively recent 

 derivative condition, in a manner parallel to that suggested above for 

 testing the primitive nature of duplication for the ligula-character in 

 Avena, namely, by means of crosses between Bursa Heegeri and the 

 oldest races of B. bursa-pastoris which can be found; for if my hypoth- 

 esis is correct, such crosses would probably result in 3 : 1 ratios in F 2 . 

 I am now seeking evidence along this line by new crosses with B. bursa- 



