104 
ORGANOGRAPHY. 
BOOK 1. 
succulent, or from the non-developemenl of it when they 
become membranous^ or from the total suppression of it, and 
even of the veins also in great part, as in those which are 
called ramentaceous, such as the primordial leaves of the 
genus Pinus. 
1 have dwelt thus much at length upon the structure of the 
leaf, because it is by far the most important part of a plant, 
and that of which the functions are the best ascertained. Let 
us next turn our attention to the modifications of the leaf. 
It has already been seen that a leaf may consist of two 
distinct parts ; the petiole, or stalk, and the lamina, or blade : 
both of these demand separate consideration. 
The BLADE, lamina, or limhus, as it is called by some, is 
subject to many diversities of figure and division ; most com- 
monly it forms an approach to oval, being longer than broad. 
That extremity of the blade which is next the stem is 
called its base ; the opposite extremity, its apex ; and the line 
representing its two edges, the margin or circumscription. 
If the blade consists of one piece only, the leaf is said to 
be simple, whatever may be the depth of its divisions : thus, 
the entire blade of Box, the serrated blade of the Apple, the 
toothed blade of Coltsfoot, the runcinate blade of Taraxacum, 
the pinnatifid blade of Hawthorn (which is often divided 
almost to its very midrib), are all considered to belong 
to the class of simple leaves. But if the petiole branches 
out, separating the cellular tissue into more than one distinct 
portion, each forming a perfect blade by itself, such a leaf is 
often said to be compound, whether the divisions be two, as in 
the conjugate leaf of Zygophyllum, or indefinite in number, 
as in the many varieties of pinnated leaves. Nevertheless, a 
more accurate notion of a compound leaf is found to consist 
in its divisions being articulated with the petiole, by which it 
is much better distinguished from the simple leaf than by the 
number of its divisions. Thus, the pinnated leaf of a Zamia, 
and the pedate leaf of an Arum, both in this sense belong to 
the class of simple leaves ; while the solitary blade of the 
Orange, the common Barberry, &c. are referable to the class 
of compound leaves. This distinction is of some importance 
to the student of natural affinities; for, while division, of 
whatever degree it may be, may be expected to occur ni 
