162 COMPOSITION OF LEAVES. 
either divide afterwards in a forked manner (jig. 319), or their 
terminal ramifications are thus divided. Such a variety of vena- 
tion has therefore been called Furcate or forked. 
The leaves of these three great divisions of plants present us, 
therefore, with three different varieties of venation: thus, those 
of Dicotyledonsare reticulated ; those of Monocotyledons parallel ; 
and those of Cormophytes forked. But the venation of Cormo- 
phytes is not so generally characteristic as that of Dicotyledons 
and Monocotyledons. 
Composition.—Leaves are divided into simple and compound. 
Thus a leaf is called simple if it has only one blade (figs. 308 
and 309), however much this may be divided, so that the divi- 
sions do not extend to the midrib (fig. 325), or petiole (figs. 
331 and 332) ; or in some cases the divisions may even extend 
to the midrib, or petiole, but the leaf is still called simple when 
the parts into which the lamina is divided are attached by a 
broad base, as in fig. 326. (See Incision, page 165.) A leaf is 
termed compound, when the petiole divides so as to separate the 
blade into two or more portions, each of which bears the same 
relation to the petiole as the petiole itself does to the stem or 
branch from whence itarises (fig. 275). The separated portions 
of acompound leat are then called leaflets or 
Fic, 320,  Jfolioles ; and these may be either sessile (figs. 
364-366), or have stalks (fig. 378), each of which 
is then termed a petiolule, stalklet, or partial 
petiole, and the main axis which supports them, 
the rachis or common petiole. 
The leaflets of a compound leaf may be 
generally at once distinguished from the sepa- 
rate leaves of a branch, from the fact of their 
being all situated in the same plane ; there are, 
however, to this character many exceptions. 
Another mode of distinguishing a simple from 
a compound leaf arises from the fact that a 
simple leaf has never more than one articula- 
tion, which is placed at the point where it joins 
the stem ; but a compound leaf frequently pre- 
sents two or more articulations: thus, besides 
Fig, 320, Leaf of the common articulation to the stem, each of 
Orange (Citrus the separate leaflets may be also articulated to 
stele the common petiole. (See also page 180.) This 
articulatedtothe character frequently forms a good mark of dis- 
lamina, 1. tinction between simple and compound leaves, 
for although it is quite true that many com- 
pound leaves only present one articulation, and can then only be 
distinguished from those simple leaves which are divided to 
their midribs or petioles by the greater breadth of attachment 
of the divisions in the latter instances ; yet, if such leaflets are 
ratciulated to the common petiole, their compound nature is 
