. Class-livre de botanique : être présente de la structure, la physiologie et la classification des végétaux ; avec une flore des États-Unis et du Canada. Botanique ; plantes ; les plantes. 64 FORME OU FIGURE. 259. De la nervation réticulée, l'étudiant devrait noter soigneusement trois formes principales, la plume, la nervation palmée, à pâte persillée et la triple nervure. La plume (à pâte persillée pinni nervure) feuille est celui dans lequel la nervation est constitué d'une nervure principale, donnent à des intervalles et des veinules latérale- vcinulcts Direction générale de l'ing. Ex. hêtre, châtaignier. 260. Dans l'émettre de nervure (palmi nervure) la feuille venation con- siste de plusieurs

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. Class-book of botany: being outlines of the structure, physiology and classification of plants; with a flora of the United States and Canada. Botany; Plants; Plants. 64 FORM OR FIGURE. 259. Of the reticulate venation, the student should carefully note three leading forms, the feather-veined, the palmate-veined, and the triple-veined. The feather-veined (pinni-veined) leaf is that in which the venation consists of a midvein giving off at intervals lateral veinlets and branch- ing vcinulcts. Ex. beech, chestnut. 260. In the radiate-veined (palmi-veined) leaf the venation con- sists of several veins of nearly equal size, radiating from the base towards the circumference, each with its own system of veinlets. Ex. maple, crow-foot. 261. The tripli-veined seems to be a form intermediate between the two others when the lowest pair of veinlets are conspicuously stronger than the others above them towards the apex, extending with the midvein towards the Summit. 262. In parallel-veined venation the veins are either straight, as in the linear leaf of the grasses, curved, as in the oval leaf of the orchis, or transverse as in the Canna, Calla, &c. FOKH OK FIGURE. 114. 110 118 Forms of leaves. 110, Rhododendron maximum. Ill, Alnus glutinosa (cult.). 112, Poly- gonum sagittatum. 113, Pawpaw. 114, Impatiens fulva. 115, Celtis Americana. 116, Circaea Lutetiana. 117, Catmint. US, Solidago Canadensis—a triple-veined leaf. 263. That infinite variety of beautiful and graceful forms for which the leaf ia distinguished becomes intelligible to the student only when viewed in connection with its venation. Since it is through the veins alone that nutriment is conveyed for the development and extension of the parenchyma, it follows that there will be the greatest extension of outline when the veins arc largest and most numerous. Consequently the form of the leaf will depend upon the direction of the veins and the vigor of their action in developing the intervening tissue. In our desc

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