420 



THE AMERICAN NATURALIST [Vol. XLIV 



One of these pure green- stemmed varieties was 

 crossed on one of the heterozygous purples, and thirteen 

 seedlings were obtained. Six plants were purple- 

 stemmed and seven were green-stemmed. This result is 

 what would be expected when crossing DR X R- 



COLOE IN THE FLOWERS 



All potato flowers have a ray of yellow extending from 

 the limb of the corolla toward the apex of each lobe. 

 The remainder of the corolla is either white or purple. 

 There is wide zygotic (in potatoes, therefore, varietal) 

 variation in the intensity of the purple sap color, but the 

 flowers should probably be classed as either purple or 

 white. The fact that the variety color, whether light or 

 dark, remains true when propagated asexually, does 

 not necessitate more than one Mendelian pair. It is 

 undoubtedly a quantitative difference in the same pig- 

 ment which is kept constant by the asexual method. 

 Why somatic cell divisions should reproduce a color 

 shade so exactly, while sexual reproduction gives rise to 

 varying shades is unknown. It is the more peculiar 

 since in animals visible division of the chromatin ap- 

 pears to be much more accurate in the sexual cells than 

 in the somatic cells. The somatic cell appears to have 

 the power of developing and of regenerating only the 

 quantity of color originally apportioned to it, except on 

 the rare occasions when all of -the potential color activ- 

 ity goes to one daughter cell and the other is left with- 

 out it. When this occurs, branches resulting from the 

 descendants of the second cell are " sports" or "bud- 

 variations" in which the original character is lost. 



Only two varieties of potatoes with flowers other than 

 purple or white have been noticed. The varietv Hol- 

 land fleur de June has blossoms which are decidedly yel- 

 low. Several attempts to self this variety and to cross 

 it with other varieties failed. One other variety, a 

 nameless seedling of unknown origin, possessed a true 

 blue flower. Xo admixture of red which would give it a 



