... lettuce plant the flowers do not mature all at once, instead they mature sequentially. The expansion of the pappus from the beak of the seed, called feathering, signals seed cluster maturation. ... with leaves away from the ground, or if the leaves are lying prostrate on the ground. Head type. The degree of heading and tightness of the head can be evaluated at the time of vegetable harvest. ... shattering, sprouting of seeds in the seed heads, and encourage discoloration and diseases of the seed. Higher temperatures and the longer daylength of summer often accelerate flower initiation...