102 BOTANICAL GAZETTE [SEPTEMBER 
that the results are due merely to a segregation of those size 
factors which control fruit thickness and fruit width. That 
such an explanation is scarcely tenable, however, is indicated by a 
study of the actual dimensions in the F., for here we find that the 
squashes which are the longest (thickest) are also those which are 
narrowest (thus producing the sphere types), and that the squashes 
which are thinnest are also those which are widest (thus producing 
the disc types). The frequency distribution of the actual lengths 
and the actual widths of the F, fruits in pedigree 19 are set forth in 
fig. 3. That part of each curve which consists of individuals which 
are spherical in shape is shaded, the discs remaining white. In fruit 
length there is evidently a fairly clear segregation into long and 
short, but no segregation is apparent in width. It is noteworthy, 
however, that the long fruits are not scattered irregularly through 
the various widths, as would be the case if length and width segre- 
gated independently, but that in practically all cases these long 
fruits are considerably narrower than the average, and the short 
fruits wider than the average, so that instead of a great variety of 
types in two rather vague groups, two very distinct shapes result. 
There is evidently something controlling the dimensional propor- 
tions which the individual exhibits, and thus determining its shape. 
The relation between these shape factors and those which control 
size is a matter of considerable interest. The suggestion is perhaps 
worth considering that the ordinary “‘size’”’ factors govern in some 
way the total amount of growth attained, and that the shape factors 
control the distribution and proportions of this growth. 
Summary 
1. Pure lines of summer squashes differing in fruit shape have 
been isolated. 
2. In crosses between a type with approximately sphericai fruits 
and three different races having ‘‘scallop” or ‘‘disc”’ fruits, the disc 
shape showed complete dominance in the F, in every case, and in the 
F, there was a sharp segregation into three-quarters disc fruits and 
one-quarter sphere. A single, large, dominant flattening factor 
thus seems to distinguish these disc types from the spherical ones. 
