316 



Gene Action 



if they grow at the same rate for all dimensions. If, however, 

 one developing ovary grows more rapidly in length, whereas 

 length and width grow at the same rate in a second type or 

 the second race grows more rapidly in width, the two fruits will 

 have a very different shape when mature (Fig. 88). 



1000 



0.1 /I 10 100 



Width (mm) 



Fig. 88. Developmental lines showing differences in relative growth of 

 length and width in various cucurbit fruits. Lines 6, 103 and 125 are 

 Cucurhita Pepo. "Zucca" and "bottle" are varieties of Lagenaria vulgaris. 

 Trichosanthes is the "snake gourd." (From Sinnott in the American 

 Naturalist.) 



In Cucurhita Pepo the relative growth rates of the length and 

 width of the fruit are almost equal and large fruits have almost 

 the same shape as small ones. In the ''bottle" gourds growth 

 is considerably faster in width, and the fruits become increas- 

 ingly wider the longer they grow; but the "Hercules club" or 

 "zucca" fruits grow more rapidly in length. In contrast to 

 the disc and sphere fruits, the genes that produce differences in 

 the shape of the bottle and zucca types act after the ovary is 

 formed and throughout subsequent development. 



In Cucurhita Pepo, where length and width increase at al- 

 most the same rate, the spindles of the dividing cells are 

 oriented in all directions approximately equally. In Lagenaria, 



