740 THE AMERICAN NATURALIST [Vol. XLIV 



sweet pea. . . . Dwarfness is plainly such a discontinuous variation in 



from that of ordinary variations in height. The former is a discon- 

 tinuous variation. Alendelian in its inheritance; the latter belongs to a 

 series of continuous variations, and is blending in its inheritance. 



While, in case of most of the crosses that I have 

 studied where the parents differ in size, the F 5 indi- 

 viduals show an intermediate size, in no case have I ob- 

 served anything corresponding to Castle's results with 

 rabbits or Lock's results with corn. In every case with 

 which I am acquainted, there has been segregation of 

 size characters in F 2 following a " blend" in F v The 

 cases in which this behavior has been studied most care- 

 fully are: size and shape of fruits of summer squashes 

 and gourds, varieties of Cucurbita pepo; size and shape 

 of bean seeds, Phaseolus vulgaris; size of grains and 

 height of stalks of Zea mays. 



Size of Maize Grains. — Queen's Golden pop corn, hav- 

 ing small grains, was crossed with Black Mexican sweet 

 corn, having grains of medium size. The grains of Fj 

 plants are intermediate between the parents in size and 

 show no more variation in size than do the grains of the 

 parent plants. 5 F 2 grains, as regards size, while uni- 

 form for any one plant, show marked variation be- 

 tween different plants. The actual measurements can 

 not be reported at this time, but an examination of the 

 material on hand shows that there are some ears with 

 grains fully as large as those of Black Mexican, others 

 with grains quite as small as those of Queen's G-olden, 

 still others whose grains are about the size of the F x 



s On ears of F x plants of this cross there are of course about three smooth 

 starchy grains to one wrinkled, sugary grain. While, on account of ' ' double 

 fecundation," the endosperm, like the embryo, of F, plants is to be regarded 

 as F 2 , exhibiting the ordinary F 2 segregation, the size of grains is a plant 

 character and to be regarded as F,. The wrinkled grains are apparently of 

 practically the same size as the smooth ones, though there is probably con- 

 where one parent is sugary and the other starchy, it would be advisable to 



starchy, "xenia," grains produced through cross-pollination by the starchy 

 parent. It would doubtless be better, however, to avoid this difficulty by the 

 use of only starchy or only sugary parents. 



