So TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 



Preliminary Note on the Shapes of Leaves. 



By G. F. Scott Elliot, M.A., B.Sc, F.L.S., F.R.G.S. 



[Read 29th December, 1896.] 



Names of the different shapes of leaves occupy so much space in 

 all text-books of botanv that it is somewhat remarkable to find 

 that very little is known as to the reasons of these shapes, of the 

 cause of these variations, or of any geometrical idea underlying 

 their complexities. 



In a general Avay, the aim of a leaf in a temperate climate is to 

 obtain as much sunlight as possible. An excellent paper by Sir 

 John Lubbock (Floicers, Fruits, and Leaves, London, 1888) clearly 

 brought out this principle, namely, that the leaves on a tree 

 supplement and do not interfere with one another. The whole 

 set fit into one another's vacancies in such a mauner as to form 

 a nearly perfect light-catching surface or screen. 



This principle, in a temperate country, cannot possibly be con- 

 troverted, and must underlie all future work on the subject. 



We may divide leaves roughly as follows : — 



1. Circular or orbicular leaves. 



2. • Elliptic, rotundate, oval, or leaves which are broadest in 



the middle. 



3. Obovate, oblanceolate, ikc, i.e., broadest towards the apex. 



4. Ovate, lanceolate, d:c., i.e., broadest towards the base. 



5. Palmate, such as the Ivy leaf. 



All these types are, of course, connected by various transitional 

 forms. The type 3, or obovate leaf, is in some respects the 

 simplest. I shall first take the rosette type of plant, which has all 

 its leaves radical and has no internodes. This is a very common 

 form, and is apparently a very ancient or primeval design. It is 

 obvious that the bases must be wedge-shaped and fit into one 

 another, whilst the outer edge may not improbably be circular in 

 outline. The most usual number of leaves in the complete leaf- 

 spiral, before a leaf is reached which is directly above the starting- 



