80 ‘TRANSACTIONS, NATURAL HISTORY SOCIETY OF GLASGOW. 
Preliminary Note on the Shapes of Leaves. 
By G. F. Scorr Exuior, M.A., B.Sc., F.LS., FE.R.G.S. 

[Read 29th December, 1896.] 
Names of the different shapes of leaves occupy so much space in 
all text-books of botany 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 way, the aim of a leaf in a temperate climate is to 
obtain as much sunlight as possible. An excellent paper by Sir 
John Lubbock (Flowers, 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 manner 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. 
Obovate, oblanceolate, &c., z.¢., broadest towards the apex. 
Ovate, lanceolate, &c., 2.¢., broadest towards the base. 
. Palmate, such as the Ivy leaf. 
oe 
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- 

