Monthly Microscoplcan 
Journal, March 1. 1869.J 
Boyal Microscopical Society, 
155 
II. — On the Composite Structure of Simple Leaves. 
By John Gorham, M.K.C.S. 
{Read hifore the Koyal Microscopical Society, November 11, 1868.) 
(Communicated by Jabez Hogg, Hon. Sec. R.M.S.) 
Plate. V. 
The results of my researclies on the Leaf Structure are so at vari- 
ance with those of the botanists, that I have hesitated in giving 
them pubhcity. They have stood in abeyance therefore for months. 
Every fresh observation, however, only tends to confirm me in their 
correctness. Under this impression I have at length ventured to 
ventilate them, and am glad to be able to do so under the auspices 
of the Eoyal Microscopical Society of London. 
If we take any compound leaf, say that of the common Horse- 
chestnut, and, detaching leaflet after leaflet until the stalk is 
denuded, examine each of them in succession, it will be found that 
in their form, but especially their venation, they are all alike. They 
vary, it is true, in their size and the angular divergence of their 
veins, but, for the most part, it will be seen that they are so nearly 
fac-similes of one another, that what is true of one is predicable of 
all the rest. Hence we may safely infer that a compound leaf is a 
multiple of similar structures. 
If we now take a supra-decompound leaf, say that of Common 
Hemlock (Conium maculatum), and carefully examine every pinnule 
with a lens, it will be discovered that all the pinnules are exactly 
alike — that they are each of them provided with a midrib which 
has its own particular set of veins, and that they are in fact of 
the nature of little leaves, which may not inappropriately be called 
typical leaflets, inasmuch as, so far from resulting from divisions of 
an otherwise supposed entire leaf, they are in reality model forms, 
typical representatives of which, by repetition, the whole leaf is 
constructed. 
This feature is of more importance than might at first sight be 
apparent. It not only enables us to acquaint ourselves with the 
internal organization of the whole of the leaf by examining an 
infinitesimal part — a single leaflet, for instance, in ordinary com- 
pound leaves, a single pinnule in supra-decompound, but it enters 
largely and conspicuously into the composition of simple leaves, in 
one section of which the structures are not only repeated, but, as 
will be shown, apparently joined at their edges, so that what has 
hitherto been considered as a simple leaf merely, is really composed 
of a series of similar typical leaflets, which, by coalescence at their 
