[Reprinted from THE AMERICAN NATURALIST, Vol. XLIL, July, 1908. 



A NEW MENDELIAN BATIO AND SEVERAL . 

 TYPES OF LATENCY 



DR. GEORGE HARRISON SHULL 



STATION FOR EXPERIMENTAL EVOLUTION OF THE CARNEGIE INSTITUTION, 

 COLD SPRING HARBOR, N. Y. 



INTRODUCTION 



IN two papers presented before the Botanical Society 

 of America at its annual meetings in New Orleans (1905) 

 and New York (1906), I discussed the question of latency 

 as exemplified by certain color-characters in common 

 garden beans (Phaseolus vulgarls). These papers were 

 published in reversed order in SCIENCE, May 7 and 24, 

 1907. 



It was shown that certain characters appeared in the 

 hybrids, of which no indication was feund in either 

 parent, and the origin of these novelties was traced to 

 unseen Mendelian units possessed by the white bean 

 (White Flageolet) used in the various crosses. The new 

 characteristics were a mottled color-pattern, M, and a 

 blackener or enzyme, B, which acts upon brown or yellow 

 pigments, P, to produce anthocyan, the presence of the 

 latter resulting in black or various shades of violet to 

 reddish purple seed-coats. It was assumed that the 

 brown and yellow beans used in these crosses have the 

 gametic formula, Pbm, the black bean the formula, PBm, 

 and the white the gametic formula, pBM. In crossing 

 the white bean with any of the Self-colored beans the 

 three dominant' units were brought together, resulting 



