438 BROOKLYN BOTANIC GARDEN MEMOIRS 



14 : 8 : 8 instead of 19 : 3 : 7. A nearer agreement might well have 

 been expected even with this small number of families. The dis- 

 crepancy is probably due in part to the small size of some of the fami- 

 lies. Thus among the families which were of necessity included in 

 the first section of the table there are six families, the largest of which 

 had no more than 33 individuals and if these families belonged properly 

 to the second group of the table, only i or 2 individuals of the recessive 

 type were to have been expected. That some of these small families 

 which contained no recessives, had them nevertheless potentially 

 present may be taken as a certainty. Only 5 such families need be 

 shifted from the first section of the table to the second section, to 

 bring about as perfect agreement with the expected ratio as is the- 

 oretically possible among 29 F3 families. 



A more positive demonstration of the duplication of the B factor 

 may be expected from the F3 families derived from the Bremen bio- 

 types in which the suppression of the dominant rosette characters is 

 less extensive. Further experiments involving these biotypes are in 

 progress. 



Discussion 



The discovery of a second case of duplication of determiners in 

 Bursa hursa-pastoris owes its chief interest to the facts pointed out 

 in one of my former papers (Shull, 1914), (a) that cases of actual 

 duplication of genes appears to be rare, and {h) that there is some 

 likelihood that the duplication of factors may involve "a series of 

 special genotypic phenomena." 



It will be recalled that only in the red pericarp of wheat, yellow 

 endosperm of maize, the occurrence of a ligule in oats, and of triangular 

 capsules in shepherd's-purse, was the demonstration of dimery con- 

 sidered adequate. Several new instances have been brought to light 

 more recently, and at least one of these must be admitted as fully 

 demonstrated (Ikeno, 191 7). This relates to the quantity and dis- 

 tribution of chlorophyll in Plantago major, in which two seemingly 

 identical factors, G and H, determine independently the normal full 

 green pigmentation of the plant. Either of these two factors may be 

 entirely wanting, without modifying in any way the self-green color, 

 but when both are absent, the plants are conspicuously variegated 

 with white or pale yellowish blotches and stripes, the total quantity 

 of chlorophyll being considerably reduced. 



Hallqvist (1916) has found the pinnatifid leaves of Brassica Napus 

 apparently produced independently by two factors, the recessive 

 undivided type reappearing in the F2 in only one plant in 16. As the 

 lobed plants showed considerable variation the results in F3 will be 

 necessary to confirm the author's conclusion in this case. 



