SIMPLE LEAVES.—MARGINS, 163 
at once evident. The presence of more than one articulation 
is, therefore, positive proof as to the compound nature of a 
leaf, but the absence of such articulation does not necessarily 
prove it to be simple, as is sometimes stated. We thus look 
upon the leaf of the common Orange, which consists of only a 
single blade (fig. 320, /), as compound, because its petiole, p, 
is not only articulated to the stem, but the blade is also articu- 
lated to the petiole. There are, however, numerous instances 
of leaves in a transitional state between simple and compound, 
so that it is impossible in all cases to draw a distinct line of 
demarcation between them. We shall now treat in detail of 
simple and compound leaves. 
1. Stmete Leaves.—The modifications which simple leaves 
present as regards their margins, figure or shape, form, and 
other variations of their blades, are extremely numerous ; hence 
we require a corresponding number of terms to define them. 
These terms are also applied in a similar sense to describe like 
modifications of the other compound organs of the plant which 
possess a definite figure and form, as the parts of the calyx, 
corolla, &c. ; and also to those of the stipules, and the leaflets 
of a compound leaf. It is absolutely necessary therefore that 
the student should become thoroughly acquainted at once with 
the more important modifications to which the blades of leaves 
are subject. It was thought by De Candoile that the figure of 
the lamina depended upon the distribution and length of the 
veins, and the extent of parenchyma which is developed between 
them ; the general outline or figure being determined by the 
former, and the condition of the margins by the latter. But 
although these views have been proved to be incorrect in a 
scientific point of view, still, if this be borne in mind, it is con- 
venient, to say the least, to study the almost infinite modifica- 
tions of the lamina of leaves with reference to his views, as it is 
always found that there is a mutual adaptation between the 
venation of the leaf and its general outline. We shall there- 
fore describe the various modifications of the lamina to some 
extent after this manner, and in doing so we shall divide our 
subject into five heads as follows :—1. Margins ; 2. Incision; 
3. Apex ; 4. General Outline ; 5. Form. 
1. Margins.—We have already stated that the condition of 
the margins is dependent upon the extent to which the paren- 
chyma is developed between the veins of the lamina. Thus, if 
the parenchyma completely fills up the interstices between the 
veins, so that the margins are perfectly even, or free from every 
kind of irregularity, the leaf is entire (figs. 316 and 320), as in 
those of the Orchis order. But when the parenchyma does not 
reach the margins, but terminates at a short distance within them, 
so that the margins are uneven, we have several modifications, 
which are distinguished by characteristic terms. Thus, if the 
margins present sharp indentations like the teeth of a saw, and 
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