SffiMarXTS Royal Microscopical Society. 159 
1. The simple entire leaf, as it exists in its free, uncombined 
state. 
2. The same leaf, as it is found in compound leaves. 
3. The same leaf, as it is found in simple lobed leaves. 
Compound Leaves. 
a. Related to Simple Leaves. — A simple leaf arises by its stalk 
direct from the branch. A compound leaf is a simple leaf, or a 
multiple of them, attached to a stalk which arises from the branch. 
The leaves of a compound leaf are called leaflets : they are generally 
articulated (jointed) with the stalk. This is the idea of a true 
compound leaf. There are many leaves, however, in which the 
leaflets are not thus articulated, but which are still called compound. 
Even a single leaf, if articulated with its stalk, is, strictly speaking, 
compound : the leaf of the Orange is an example. The leaflets, in a 
compound leaf, are almost invariably netted or feather-veined. If 
we take a number of compound leaves, strip them of their leaflets, 
and sort them, they will be found divided into two groups, the one 
consisting of netted, the other of feather-veined leaves. The follow- 
ing are examples of compound leaves, the leaflets of which have 
a netted venation : — Wisteria, Potato, Walnut, Ash, Virginian 
creeper, Tree of Heaven, &c. Compound leaves with feather- veined 
leaflets are exemplified in Horse-chestnut, Sumach, Hog-weed, &c. 
The association between compound and simple leaves is thus 
clearly established. 
p. Related to Lohed Leaves. — The leaflets in compound leaves 
are arranged in two ways on their leaf-stalk — (1) in a ray diverging 
from the summit of the stalk, as in Horse-chestnut ; (2) in a row on 
either side of an elongated petiole, as in Ash. So are the leaflets in 
lobed leaves. 
The leaflets in compound leaves all expand in one plane. So do 
those of lobed leaves. 
They vary in their dimensions, especially in their relative 
lengths, by which the outline of the entire leaf is determined. So 
do the leaflets in a lobed leaf. 
They are arranged for the most part symmetrically on the sides 
of the stalk. So are the leaflets in a lobed leaf. 
They are all separate^ not united at their edges. It is here that 
the link between the two classes appears at first sight to be broken. 
This is more apparent, however, than real ; for it can be shown that 
the two classes merge the one into the other by easy transition, and 
this through an interesting series of compound leaves which have 
sufiered metamorphosis. For the leaflets in compound leaves are 
not always separate ; they will be found to have contracted union at 
their edges in a group which has hitherto been considered insignifi- 
cant, mere " lusus naturae," or sports, and which have been treated in 
