MORPHOLOGY, GENETICS AND BREEDING 55 



At the same time, the polar nuclei fuses with the second sperm nucleus. 

 The primary endosperm nucleus resulting from this triple fusion divides 

 first, usually within 8 to 12 hours after fertilization. The zygote has 

 usually divided to form a two-celled embryo within 36 hours. 



During the first 10 to 12 days after flowering", growth proceeds slowly 

 in both embryo and endosperm, but in this same period the peg, after a 

 slow start, grows rapidly and usually approaches or reaches the soil 

 surface. From the fifth to the tenth day of fruit development, the growth 

 and elongation of the peg accelerate rapidly. During this same period 

 cell and nuclear divisions are virtually absent in the embryo and endo- 

 sperm (Smith, 68). After the tenth day, both embryo and endospferm 

 begin to grow rapidly in normally developing seeds, concurrently with 

 the beginning of underground pod enlargement. The durations of the 

 early stages of both peg and seed development vary widely as a result 

 of position on the plant, competition with other fruits, and other environ- 

 mental circumstances. 



More than 93 percent of the eggs have been reported as fertilized 

 and about 12 percent of the early embryos as aborting during the first 

 two weeks of growth (Smith, 67). As most of the fertilization failures 

 or embryo abortions occurred singly in the apical ovules, approximately 

 14 percent of the pegs studied contained a single developing seed in the 

 basal position. This value is compared with 18 percent one-segmented, 

 one-seeded pods which were harvested in the control sample. Failure of 

 fertilization and early embryo abortion appear to account for the occur- 

 rence of most of the one-seeded fruits so frequently seen. 



It is equally evident from these results that normal megasporogenesis, 

 embryo sac development, and fertilization provide no basis for predicting 

 the occurrence of the later seed failures which give rise to the shriveled 

 seeds and empty pods characteristic of the pop condition. When a young 

 seed fails during the peg stage, the portion of the ovary containing it also 

 fails to grow. Failures of the seed after underground pod enlargement has 

 begun do not seem to inhibit the completion of pod development. Thus, 

 recent data (68) are in harmony with the conclusions of Burkhart and 

 Collins (15) and of Colwell and Brady (18) that calcium deficiency in 

 the fruiting zone of the soil is a principal cause of the "pop" condition. 



Flowering and Fruiting 



Peanut flowers begin to appear 4 to 6 weeks after planting. Richter 

 (59) observed that in contrast to flowers of most plants, those of peanuts 

 are most abundant on the lower nodes. He considered this an adaptation 



