452 



STRUCTURE AND LIFE HISTORIES 



Fig. 336. — Effect of self-pollination in the blueberry {Vacciniiim corym- 

 bostim), as compared with cross-pollination. These two twigs, both 

 natural size, were in equally good situations on the same bush, contained 

 the same number of flowers, all pollinated by hand at the same time with 

 equal care, and the fruits were photographed on the same day. The only 

 difference in treatment was that the pollen used on the left-hand twig 

 came from other flowers on the same bush, while the pollen for the right- 

 hand twig was taken from another bush. The cross-pollinated flowers 

 produced a full cluster of handsome fruit. The self-pollinated flowers 

 produced no ripe fruit, all the fruit that set remaining small and green and 

 later dropping off, until at the time the photograph was taken only two 

 such imperfect fruits remained. A plantation made up wholly from cut- 

 tings from a single bush would produce little or no fruit. At least two 

 original propagation stocks are necessary. (After Coville. Courtesy of 

 the U. S. Dept. Agric.) 



