LEAVES. 
b. Some plants are destitute of leaves ; they are then called Ap1iyVl<yus,fi^t& 
the Greek a, to want, phyllon, a leaf. 
c. Specific names are often given from some circumstance of the leaf: the Hepati- 
CA triloba is that species of the Hepatica which has leaves with three divisions, called 
lobes. The viola rotundifolia, is a species of violet with round leaves. A knowl- 
edge of the various appearances presented by leaves is of great importance to the 
botanical student ; in order to become acquainted with these, much practice in the 
analysis of plants is necessary. Engravings will assist the pupil in undt.rstanding 
definitions, but i^ature should ever be consulted when piacticable. 
52. The new plant is called 2ipliyton; in its simplest form it 
consists of two leaves and a bud, which is the axis, and forms 
the stem and root. Seminal leaves first appear above the sur- 
face of the earth, as in the garden bean ; these leaves are the 
cotyledons, which, after nourishing the phyton, decay. Pri- 
mordial leaves appear in the axils of the seminal leaves, and re- 
semble them in position, form, and size. The primordial leaf, 
according to the fanciful idea of a French botanist, is a sketch 
which nature makes before the perfection of her work. CTiar- 
aoteristiG leaves are found in the mature state of the plant. 
According to the idea above advanced, nature here perfects 
her design. It is not always, however, that this process, with 
regard to change of leaves, takes place ; as in many cases, the 
proper, or characteristic leaf, is the only one which appears. 
53. Yenation of Leaves. — ^The expanded part of the leaf is 
called the lamina or blade ; the end of the blade next the stem 
is the hase^ the opposite end the apex, TTie jpa/renchyma is the 
cellular tissue which composes the body of the leaf, or the fill- 
ing of a frame-work or skeleton composed of 'vascular tissue. 
The bundle of vessels which compose this frame-work are called 
veins^ sometimes ribs and ne^'ves. The midrib is the principal 
vein which passes from the leaf-stalk through the center of the 
leaf; its branches slyq primary y ems ^ which, when subdivided, 
are called secondary veins, and a still more minute division, 
veinlets. The distribution of veins in the leaves is called vena- 
tion^ sometimes nervation. Jii succulent plants the veins are 
sometimes obscure; these are called hidden-veined. Leaves 
may be divided into th7'ee great classes according to theii 
venation. Beticulate or netted leaves, in which the petiole is 
prolonged into the leaf in the corm of the midrib, and there is 
an angular net-work of vessels, as occurs in the leaves of ex- 
ogenous plants, as the oak, rose, &c. Parallel-Reined^ in which 
the veins run in a straight or curved manner from base to apex, 
or from the midrib to the margin of the leaf, and are connected 
by simple transverse veins, as appears in most endogenous or 
monocotyledonous plants, as the lily, grasses, &c. Porhed 
veined^ when the veins divide and subdivide by forked divi- 
b. Aphyllous plants — c. Leaves furnish specific characters. — 52. Leaves with respect to succession -- 
53. Venation of leaves— Reticulate-veined— Parallel-veined— Forked-veined— Feather, and radia»» 
veined 
