Sinnott and Durham: Summer Squash 



183 



times thrown smooth or nearly smooth 

 types when inbred, thus suggesting 

 that wartiness is dominant over 

 smoothness. Wartiness is not a simple 

 character, however, for it shows all 

 degrees of development from one or 

 two small spots to a surface completely 

 covered with warts. It is very difficult 

 to grade these types satisfactorily, 

 so that in the records here presented 

 they are all grouped together as 

 "warty." The results of five crosses 

 are set forth in Table III. 



In pedigrees 1 and 8, a single factor 

 difference between warty and smooth 

 will evidently explain our results, there 

 being 126 warty plants to 44 smooth 

 ones in the F2. It is noteworthy that the 

 warty parent in both these cases was 

 only moderately warty. In pedigrees 

 13, 18, and 22, on the other hand, there 

 is a great deficiency of smooth plants 

 in F2, and a much closer approach to a 

 15:1 ratio than to a 3:1. The warty 

 parents in these three cases were 

 extremely warty, much more so than in 

 the first two pedigrees. In the Fo, 

 wartiness was present in all degrees, 

 but it was noticeable that plants as 

 extreme as the original warty parent 

 were rare and that the great majority 

 resembled the Fi in being only moder- 

 ately warty. In these cases, wartiness 

 seems to be caused by two independent 

 factors, cumulative in their effect. 



The pure types which show an inter- 

 mediate degree of wartiness evidently 

 possess only one of these factors. 



FRUIT SHAPE 



Evidence as to the manner of inheri- 

 tance of fruit shape in these crosses has 

 been presented elsewhere in some detail 

 by the senior author,^ but may be 

 briefly summarized here. Most of the 

 pure lines isolated showed the "scal- 

 lop," (patty pan), or disc type of fruit, 

 much broader than long (Figs. 17 and 

 18). In two of these lines there 

 several times appeared, as a result of 

 inbreeding, plants with fruits almost 

 spherical in shape (Fig. 18, 45AS5, 

 Fig. 17, 13AS). These forms sub- 

 sequently all bred true, thus sug- 

 gesting that the spherical type is 

 recessive to the disc. Four crosses 

 between the disc and the sphere shapes 

 were made, the results of which are 

 presented in Table IV. 



These factors show clearly that there 

 is a single factor difference between 

 disc and sphere, the F2 ratio being 

 almost exactly 3:1 (254:85). The disc 

 shape is completely dominant, the Fi 

 showing no trace of thickening. The 

 extracted F2 spherical plants, however, 

 are not all alike but show an effect 

 derived from the disc parent, those 

 coming from crosses in which the disc 

 parent was relatively flat being some- 



Table III. Inheritance of Fruit Surface 



Table IV. Inheritance of Fruit Shape 



3 Sinnott, Edmund W., The Inheritance of Fruit Shape in Curcurbita pepo. Bot. Gazette, 

 LXXIV:95-103. 1922. 



