566 BOTANY OF CROP PLANTS 



proportionate to the sexual development of the plant; that 

 the most degenerate tuber is produced on the plant which 

 carries fully developed flowers and virile pollen; while those 

 plants on which only female portions of the flowers appear to 

 be fully developed, produce tubers intermediate in form and 

 yield, and that the best tubers and the largest yield are pro- 

 duced by the type of plant whose flower buds do not even 

 swell." Furthermore, these buds do not show any other 

 color than green and they soon wither and break off. 



Fruit. — The fruit (Fig. 233) is a globular or short oval 

 berry with two locules containing numerous seeds attached 

 to the thick axil placenta and embedded in a green acrid 

 pulp. The fruit is called by various names, such as "potato 

 ball," "potato apple," or "apple," but is commonly referred 

 to as the " seed ball." In color the seed balls are brown, 

 purplish green, or green tinged with violet. Single fruits may 

 contain from a few to as high as 200 or 300 seeds, but some- 

 times no seeds are produced. Fitch found no seeds in 650 

 seed balls of Early Rose. One seed ball from a Pearl crossed 

 with a Rual contained no seed, while six seed balls of the 

 reciprocal cross all bore abundant seeds. Removal of the 

 early tubers induces fruit-bearing, while removal of the 

 flowers is said to encourage tuber development. 



Seed, — The seeds are small, kidney-shaped, and embedded 

 in the green, very acrid pulp of the fruit. 



Germination of Seed. — Potatoes are seldom propagated by 

 seed except for the production of new varieties. As a result, 

 many who are familiar with tuber propagation know little or 

 nothing about seed germination. 



Germination of seed begins in about five to seven days after 

 planting, being complete in about eleven to sixteen days. 



Fig. 233. — Potato seed balls, showing a cluster, and lateral, sectional and 

 basal views. (After Stuart, U. S. Dept. of Agri.) 



