. Une classe-livre de botanique, conçu pour les établissements, les académies, et d'autres séminaires. Illustré par une flore du nord, du centre et de l'ouest des États-Unis, en particulier des États-Unis au nord de la capitale, lat. 38 3/4. Botanique ; plantes ; les plantes. 86 LA FEUILLE. sont toujours reliés par des veinules transversale simple. Ex. L'herbe lily. l. FIG. 28 - Formes de venation. 1, 2, Exogens ; 3, 4 ; Endogen, acrogen. 3d. Nervation fourchue, comme dans l'Cryptogamia, lorsque les veines se diviser et subdiviser par divisions fourchue qui ne s'unissent à nouveau. Ex. de fougères. 230. De la première sorte de, la nervation réticulée, il y a deux varietie

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. A class-book of botany, designed for colleges, academies, and other seminaries. Illustrated by a flora of northern, middle, and western states; particularly of the United States north of the Capitol, lat. 38 3/4. Botany; Plants; Plants. 86 THE LEAF. are always connected by simple transverse veinlets. Ex. grass lily. l. FIG. 28 — Forms of venation. 1, 2, Exogens; 3, Endogen; 4, acrogen. 3d. Forked-veined, as in the Cryptogamia, when the veins divide and subdivide by forked divisions which do not unite again. Ex. ferns. 230. Of the first kind of venation, the reticulate, there are two varieties which deserve the most careful attention. The feather-veined and the radiate-veined. 1. The feather-veined leaf is that in which the venation con- sists of a midvein, giving off at intervals lateral veinlets and branching veinulets. Ex. beech, chestnut. 2. In the radiate-veined, the venation consists of several veins ( $ 227) of nearly equal size, radiating from the base towards the circumference, each with its own system of veinlets and veimilets. Ex. maple, crow-foot. 3. In parallel venation, the veins are either straight, as in the linear leaf of the grasses, curved, as in the oval leaves of the Orchis, or transverse, as in the Canna, Calla, &c. §4. FORM OR FIGURE. 231. That infinite variety of beautiful and graceful forms for which the leaf is 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 where the veins are largest and most numer- ous. 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. For this interesting theory we are indebted to Alphonse De Candolle.. Please note that these images are extracted from scanned page images that may have b

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