249 



On the Development and Morphology of the Leaves of Palms. 



By Agnes Arbee, D.Sc, F.L.S., Keddey Fletcher-Warr Student of the 

 University of London. 



(Communicated by Prof. F. W. Oliver, F.R.S. Received October 8, 1921.) 



CONTENTS. 



PAGE 



I. Introduction 249 



II. The Ontogeny of the Palm Leaf 251 



1. The " Plicated " Limb 251 



2. The Membrane ("Coiffe") 254 



3. The Terminal " Gland " 255 



4. The " Ligule " and " Dorsal Scale " 256 



III. The Morphological Nature of the Palm Leaf 257 



IV. Summary 260 



Acknowledgments 261 



List of Memoirs Cited 261 



I. Introduction. 



In series of previous memoirs* I have discussed the phyllode theory of 

 the Monocotyledon ous 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 Hues 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 pmnate 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. 



The morphological value of the various members which constitute the 

 Palm leaf will be discussed in a later section of this paper (pp. 257-60). 



It has long been known that the " compound " appearance of Palm leaves 

 is the result of secondary changes, and that these leaves are thus not truly 

 equivalent to the divided or compound leaves of Dicotyledons. Nearly 



* Arber, A. (1921), and earlier papers there cited. 

 VOL. XCIII. — B. T 



