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occurring above ground some are underground, which are often merely disguised "stems," like the quack grass stem. Buds are really branches and bear small scales, which are only modified leaves. The bud terminating a branch is called a terminal bud. Fleshy buds are those having fleshy scales. When more than one bud occurs in the axil of the leaf, they are called accessory buds, as in the case of the butternut and honeysuckle. Buds also occur under the petiole of the leaf, as in the sycamore, and are called sub-petiolar buds. Some buds are so concealed that they cannot be seen until growth begins. These are known as latent buds. Adventitious buds are such as develop without any regular order from any part of the stem or from roots. The sweet potato root develops these adventitious buds and many plants such as the plum produce suckers from them.

The stems of grasses, lily, and onion are endogenous; the outside is the epidermis and the bundles are distributed through the mass. The stem of pigweed is exogenous, and consists of pith, wood and bark.

Fig. 39. Brace or air

Most plants of our region form a definite annual growth with a terminal bud, hickory and horse chest-, roots of corn (aerial). nut being examples of these.

Some (C. M. King.)

plants, as the grape, grow until killed by frost, whatever buds are not fully developed at that time being killed. This is known as indefinite growth.

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Fig. 40. Cross section of an endogenous stem of corn (Zea Mays). S, node; A, sheath of leaf. The small dots, the fibrovascular bundles. (C. M. King.)

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scales on the rootstock of quack grass are also modified leaves.

A typical leaf consists of a blade, the stalk or petiole, and a pair of stipules. In some cases the stalk may be wanting and the leaf is said to be sessile, in others the stipule is wanting and in a few the blade is wanting.

The blade is the expanded part R of the leaf and is for the purpose of making food. The petiole is the stalk and serves to fix it to the stem. The stipules are a pair of small scales at the base. There is great variation of the different parts of the leaf.

Fig. 41. R, R, tendrils of Japanese ivy, modified

There are two kinds of leaves as to venation. Corn and other stem.

grass leaves are parallel veined, the leaf of the canna has a similar venation. The veins or lines run parallel with

Fig. 42. x, tendril of star cucumber.

types of these, the palmately veined, when the veins start from a number of ribs, as in the grape and maple, or pinnately veined, where one rib runs through the leaf from the base to the tip, as in milkweed.

Leaves are divided into simple and compound. In a simple leaf, like the maple, there is a single stalk and a blade. In compound leaves there are several leaflets, each

each other from the

base to the end of the leaf. Plants with such venation have a single seed leaf or cotyledon.

In netted-veined leaves the veins run together or anastomose, forming a network, as in the maple, oak, and potato; all of our trees have netted-veined leaves. There are

two

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Palmately netted-veined,

Fig. 43. compound leaf of horse chestnut.

usually with its own stalklet, as in the rose. Compound leaves are of two kinds: pinnately compound, in which the leaflets are arranged on the sides of a main stalk, as in rose and ash; and palmately compound leaves, in which the leaflets are borne on the end of a leaf stalk, as in the horse-chestnut and Virginia creeper. Clover has a trifoliate compound leaf, c. g., a leaf with three leaflets. Some leaves have two leaflets, these are bifoliate. Some leaves, like the honey locust, are simply pinnate, but occasionally on young shoots they are divided again; these, then, are twice pinnate. The palmately compound leaves of meadow rue are in threes or ternately compound, or four times compound. When a leaf is twice compound it is biternate.

Fig. 44. Pinnately netted-veined leaf of rose. (Ada Hayden.)

There are many different forms of

leaves, the more important being as follows: Linear, a narrow leaf much longer than broad, like blue grass; lanceolate, a leaf which is longer than broad, tapering toward the apex, outline lance-shaped; oblong, when longer than broad; elliptical, like an oblong leaf, but the ends of the same width; ovate, longer than wide, the base wider than the end, like a hen's egg in outline; orbicular, circular in outline; oblanceolate, like a lanceolate leaf, but the apex wider than the base; spatulate, shaped like a spatula, apex rounded; obovate, like an ovate leaf, but the apex wider than base; cuneate,

Fig. 45. Parts of a leaf; s, stipules; P, petiole; b, blade.

a wedge-shaped leaf; cordate, leaf with a wide and rounded base, forming a notch where the petiole is attached; reniform or kidney-shaped leaf, like the leaf of wild ginger; auriculate, leaf with a pair of small blunt pro

2

Fig. 46. Two types of parallel-veined leaves.

jections at the base; sagittate, like an auriculate, but the projections are sharp, as in sagittaria; hastate, like the last, but with lobes pointing outward; peltate, the petiole attached to the lower surface, like the mandrake; acuminate, the apex of leaf prolonged into a tapering point; acute, where the leaf ends in a sharp point

rather abruptly; obtuse, where the leaf has a blunt or rounded apex; mucronate, where the apex of the leaf is tipped with a small and short point; truncate, with the end as if cut off square; retuse, where the summit of the leaf has a small notch; emarginate,

with a decided

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notch; obcordate, the reverse of cordate, the upper end

larger, like the leaf of white clover; cuspidate, leaf with a

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