. La nature et le développement des plantes. La botanique. 8 LE TRAVAIL DE LA FEUILLE plus important travail effectué par les feuilles est la construction. d'aliments, le dégageant de l d'eau ou la transpiration et la respiration ou la respiration. L'ampleur de ce travail dépasse de loin l'énergie dépensée dans toutes les industries du monde. Les feuilles, cependant, la réalisation de ce travail si doucement et économiquement que la plupart des gens sont à peine conscients. Afin de comprendre le but du pétiole et vert pale (Fig. 3) ou de l'importance des diverses formes et modalités de feuilles il sera nécessaire d'examiner

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. Nature and development of plants. Botany. 8 THE WORK OF THE LEAF more important work performed by the leaves is the construction. of foods, the giving off of water or transpiration, and breathing or respiration. The magnitude of this work far exceeds the energy expended in all the industries of the world. The leaves, however, accomplish this work so quietly and economically that most people are scarcely conscious of it. In order to understand the purpose of the petiole and green blade (Fig. 3) or the significance of the various forms and arrangements of leaves it will be necessary to examine the struc- ture of the leaf and see the character of the apparatus that is used in the performance of its work. The blades of the majority. Fig. 4. Blade of lilac leaf cut across, showing the more compact arrange- ment of cells upon the upper side of the leaf. of leaves are flat. A section through such a blade, cut as in Fig. 4 so that we can look into the end of the blade, shows that the leaf is composed of a complicated arrangement of cells. Fig. 5 is a greatly enlarged view of Fig. 4 taken at X. 4. The Epidermis.—It is now seen that a layer of compact cells (Fig. 5, e) surrounds the leaf on all sides. In fact such a layer covers all parts of the plant body. This layer of cells, the epi- dermis, is provided with minute openings or stomata (sing, stoma), Fig. 5, s. The stomata are especially abundant in the epidermis on the under surface of the leaf and often quite lacking from the upper surface. A better idea of these openings and of the epidermal cells may be gained by stripping off the epidermis. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original work.. Curtis, Carlton Clarence, 1864-1945. New York, H. Holt

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