Part 5

A =rhizome=, or =rootstock=, is a horizontal underground stem. It is sometimes thick, fleshy, or woody, as in the iris;

a =tuber= is a short, much thickened rootstock, having eyes or buds of which the potato is an example;

a =corm= is a depressed and rounded, solid rootstock; it may be called a solid bulb; the garden cyclamen is an example;

a =bulb= is a leaf-bud, commonly underground, with fleshy scales or coats; the lily is an example.

LEAVES

=Leaves= are the green expansions borne by the stem, out-spread in the air and light, in which assimilation is carried on. They may be said to be the stomachs of the plant. A typical leaf consists of three parts--the =blade=, the =foot-stalk= (or =petiole=), and a pair of =stipules=. Yet any one of these parts may be absent.

The =blade= is the expanded portion of the leaf and the part to which the word leaf, in its commonest sense, is applied;

the =stipules= are small, usually leaflike bodies borne at the base of the petiole, usually one on either side;

the =petiole= is the stalk of the leaf.

=Leaves= are =simple=, when having but one blade; =compound=, when having more than one, when each blade is called a =leaflet=.

Compound leaves are said to be--

pinnate, when the leaflets are arranged along the sides of a petiole, or rather of its prolongation, the rachis;

abruptly pinnate, with an even number of leaflets;

odd-pinnate, with an odd leaflet at the end;

palmate, or digitate, when the leaflets all diverge from the summit of the petiole, like the fingers of a hand.

VENATION

The venation, or veining, of leaves relates to the mode in which the woody tissue, in the form of ribs, veins, etc., is distributed in the cellular tissue.

There are two principle modes--

the parallel-veined, of which the iris is an example;

the reticulated-veined, or netted-veined, of which the Elm is an example.

Small veins are called =veinlets=.

FORM

As to general form, or outline, leaves are:--

Those broadest in the middle--

peltate, or shield-shaped, when rounded, with the stem attached to the center, or near it--as in the garden nasturtium;

orbicular, when circular in outline, or nearly so;

oval, when having a flowing outline, with the breadth considerably more than half the length, and both ends alike;

elliptical, when having a flowing outline, twice or thrice as long as broad, and both ends alike;