. A practical course in botany, with especial reference to its bearings on agriculture, economics, and sanitation. Botany. 156 PRACTICAL COURSE IN BOTANY. Fig. 208. —Palmately net- veined leaf of wild ginger. leaf (Fig. 208) into a number of primary veins or ribs, which radiate in all directions like the fingers from the palm of the hand; hence, such a leaf is said to be palmately veined. Net-veined leaves — the plantain (Fig. 209), wild smilax, beech, dog- wood — are sometimes ribbed in a way that might lead an inexperi- enced observer to confound them with parallel-veined ones, but the retic
. A practical course in botany, with especial reference to its bearings on agriculture, economics, and sanitation. Botany. 156 PRACTICAL COURSE IN BOTANY. Fig. 208. —Palmately net- veined leaf of wild ginger. leaf (Fig. 208) into a number of primary veins or ribs, which radiate in all directions like the fingers from the palm of the hand; hence, such a leaf is said to be palmately veined. Net-veined leaves — the plantain (Fig. 209), wild smilax, beech, dog- wood — are sometimes ribbed in a way that might lead an inexperi- enced observer to confound them with parallel-veined ones, but the reticulations between the ribs show that they belong to the net-veined class. 173. Veins as a mechanical sup- port. — Hold up a stiff, firm leaf of any kind, like the mag- nolia, holly, or India rubber, to the light, having first scraped away a little of the under surface, and examine it with a lens. Compare it with one of softer texture, like the peach, maple, or clover. In which are the veins the closer and stronger? Which is the more easily torn and wilted ? Tear a blade of grass longitudinally and then cross- wise ; in which direction does it give way the more readily ? Tear apart gently a leaf of maple, or ivy, and one of elm or other pinnately veined plant; in which direction does each give way with least resistance? What would you judge from these facts as to the mechanical use of the veins ? 174. Effect upon shape. — By comparing a number of leaves of each kind it will be seen that the feather-veined ones tend to assume elongated outlines (Figs. 197,207); the palmate-veined ones, broad and rounded forms (Figs. 195, 208). Notice also that the straight, unbroken venation of parallel-veined leaves is generally accompanied by smooth, unbroken margins, while the irregular, open meshes of net-veined leaves are favorable to breaks and Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability -
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