Morphogenetic Effects of Seasonal Conditions on Head Development of Cos Lettuce (Lactuca Sativa L. Var. Romana) Growing in a Subtropical Climate

SummaryHead development of cos lettuce growing under natural conditions was studied during the four main annual growing seasons. Two fundamental processes, the accumulation of similar-length leaves and leaf-folding, governed the heading process in all seasons, their relative or absolute contribution to heading greatly affecting the final structure and firmness of the mature lettuce head. When no bolting occurred at the end of the growing season the heads disintegrated, mainly as a result of leaves unfolding, the plant thus returning to the rosette state. This phenomenon showed that leaf folding in cos lettuce can be a reversible process.