Lettuce plants (Lactuca sativa L.) showed definite flowering peaks over a 70-day period. Over 90% of the seed yield was from flowers which opened during the first 35 days, and seed produced from flowers opening during the first 2 flowering peaks were heavier than those produced later in the season. Seed size was not correlated with number of seeds per flower head. Seed yield and quality were not affected by early harvest or by withholding water and nutrients during the last half of the flowering period. Flowering rate, seed yield, and seed quality were not related to air temperature in the range 67 to 94°F.
Received for publication September 4, 1973. This research was supported in part by a grant-in-aid from the California-Arizona Lettuce Research Corporation. Technical assistance of J. Moore, M. Rutter, L. Baker, and T. Soffer is gratefully acknowledged. This report is submitted as a partial requirement for the Ph.D. by the senior author.