. Essentials of botany. Botany; Botany. ECOLOGY OF LEAVES 115 leaf of an unknown plant whether it is an alpine, a desert, or a seaside species. This is because of the importance of leaves in disposing of the water taken into the plant (Chapter Xlli). 135. Leaves of Hydrophytes.—Not nearly all hydrophytes are aquatics, but some merely prefer very moist soil or moist air. Of the truly aquatic species some have their leaves wholly submerged; others, such as the duck- weeds and pond-lilies, have them floating; and still others, like the sedges, the bur reeds, tbe cat-tails, and the weeds
. Essentials of botany. Botany; Botany. ECOLOGY OF LEAVES 115 leaf of an unknown plant whether it is an alpine, a desert, or a seaside species. This is because of the importance of leaves in disposing of the water taken into the plant (Chapter Xlli). 135. Leaves of Hydrophytes.—Not nearly all hydrophytes are aquatics, but some merely prefer very moist soil or moist air. Of the truly aquatic species some have their leaves wholly submerged; others, such as the duck- weeds and pond-lilies, have them floating; and still others, like the sedges, the bur reeds, tbe cat-tails, and the weeds, have their leaves freely exposed to the .air. A few plants have both water leaves and air leaves (Fig. 79). It is generally supposed that the thread-like form of sub- merged leaves in so many species of aquatics gives them greater capacity to absorb dissolved gases, from the water which surrounds them. 136. Leaves of Xerophytes. —In regions where the great- est dangers to vegetation arise from long droughts and the excessive heat of the sun, the leaves of plants usu- ally offer much less surface to the sun and air than is the case in temperate clilnates, as shown in the Australian blackberry (Fig. 80). Sometimes the blade of the leaf is absent and the expanded petiole answers the purpose of a blade, or, again, foliage leaves are altogether lacking, as in. Fig. 79. Submerged and Aerial Leaves of a European Crowfoot (Banunculus Purshii). The leaf with thread-like divisions is the submerged 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 Bergen, Joseph Y. (Joseph Young), 1851-1917. Boston, Ginn
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