582 



THE AMEBIC AN NATURALIST 



[Vol. XLIX 



favorable conditions for the survival of any new forms that ap- 

 peared just as many mutations would have been found as in the 

 above experiment. In the light of these results we can attribute 

 the origin of mutations only to chance, since hybridization as a 

 causal agent does not occupy a privileged position relative to 

 the effect. 



F. N. Duncan- 

 Columbia University 



LINKAGE AND SEMI-STERILITY 

 The Florida velvet bean (Stizolnhimi) <h rriin/ianum) has nor- 

 mal pollen and embryo-sacs; it flowers (when sown in May) 

 early in September; and has pigmented (mottled) seed-coats. 

 The Yokohama bean (Stuolobium hassjoo) has also normal pol- 

 len and embryo-sacs; it flowers in July; and has its seed-coats 

 unpigmented. The first-generation hybrids of Florida by Yoko- 

 hama had half their pollen and embryo-sacs aborted (1, 2) ; 

 flowered at the end of August ; and had more or less pigmented 

 seed-coats. In the second generation, half of the plants had 

 normal pollen and embryo-sacs, and half showed semi-sterility 

 (1, 2). These plants flowered from July to September, the ma- 

 jority being late. About three-quarters had pigmented seed- 

 coats; and one-quarter, colorless seed-coats. 



Most of the semi-sterile plants, and also most of the plants with 

 pigmented seed-coats, were late in flowering. The semi-sterile 

 plants, however, were not later than the fertile, in the second 

 generation of the Florida by China cross. Hence there is no 

 necessary connection between semi-sterility and lateness. A ran- 

 dom sample of five second-generation plants of the Florida by 

 Yokohama cross gave one family with pigmented seed-coats, one 

 family with colorless seed-coats, and three families segregating 

 into pigmented and colorless in about the ratio 3:1. Hence the 

 pigmentation of the seed-coat is not a mere physiological conse- 

 quence of lateness, but is determined by a definite factor. If K 



a factor concerned with pigmentation of seed-coat; and H, the 

 main factor for lateness; then K and // are strongly coupled in 

 the gametes of the first-generation plants, as are also P and II. 

 K and P show secondary coupling. 



