The development of the unisexual male and female flowers of Zea mays from bisexual initials in both tassels and ears has been reinvestigated with SEM and TEM. The early stages of spikelet branch primordia, spikelet initiation, and early flower development are similar in both flowers, though differences in rates of growth of glumes, lemmas, and palea were detected. In both tassel and ear flowers, a pair of stamens arises opposite the lemmas and a third stamen initiates later at right angles to the first pair but from a point on the meristem below its insertion. Gynoecia develop on both tassel and ear flowers first as a ridge which overgrows the apical meristem giving rise to the stylar canal and the elongate silk. Male flowers arise in the tassel through selective vacuolation and abortion of the cells of the early gynoecium. The single female flower in each ear spikelet arises through the vacuolation and abortion of stamens in the upper flower and the repression of growth of and the eventual regression of the lower flower in each spikelet. The significance of these selective organ abortions for practical applications is discussed.

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Growth analysis indicates that the plastochron index (PI) is consistently applicable for describing the morphological status of the vegetative tomato shoot in quantitative terms, and pronounced seasonal variability in the growth habit is minimized. However, the PI is not applicable to tomato shoots after flower buds are produced at the vegetative apex. True leaf no. 3 goes through four growth stages which can be characterized in terms of the leaf plastochron index (LPI3). A basipetal trend in leaf growth and development is evident.