On the development and morphology of the leaves of palms

Abstract

In series of previous memoirs I have discussed the phyllode theory of the Monocotyledonous leaf, both in general and in relation to a number of special cases. In the present paper I propose to consider the Palms, with a view to determining whether their highly peculiar leaf structure is open to interpretation on the lines which have suggested themselves in the course of my study of other families, in which the leaves are less obviously anomalous. The mature Palm leaf consists of a closed basal sheath (sometimes continued upwards into an ochrea), a leaf-stalk, and a limb, which may be of palmate or pinnate form; the “fan” and “feather” types of limb grade into one another, the distinction depending only on the degree of elongation of the median rachis. The Fan-palms differ from the Feather-palms in one further point on which great stress is sometimes laid—namely, that they bear small excrescences at the base of the limb. The outgrowth on the ventral side is the so-called ligule; less frequently a corresponding but smaller structure, known as the dorsal scale, occurs on the opposite side.