Any attempt to study the apical meristem of the shoot, even a simple dissection to expose it for observation, leads immediately to a consideration of the initiation and development of lateral appendages, particularly leaf primordia. It is evident that the formation of leaf primordia is a major activity of the shoot meristem and that the early development of these primordia in such close proximity to the meristem must result in important developmental interactions between the two. This intimate relationship is reflected in the unity of the mature shoot system in which any attempt to isolate stem and leaf either structurally or functionally is artificial. The student of phylogeny finds an interpretation of this relationship, at least in the ferns and seed plants, in the evolution of stem and leaf from a primitively undifferentiated branching system. The object of developmental analysis, however, must be to understand how, in the individual living plant, structures that originate as outgrowths of the meristem acquire distinctive characteristics and interact with one another and with the meristem that produced them. This analysis is further complicated by the fact that the same meristem frequently gives rise to other appendages that develop as replicas of the original shoot.

Whereas the shoot is characterized by potentially unlimited or indeterminate growth and this feature is retained by lateral branches, the leaf is an organ of transient, although in some cases extensive, growth.