. Research methods in ecology. Plant ecology. 128 THE PLANT stantly below the water; in amphibious ones, they grow normally in the air. Floating plants have leaves in which the upper surface is in contact with the air, and the lower in contact with the water. Transpiration is at a maximum in the amphibious plant; it is reduced by half in the floating type, and is altogether absent in submerged plants. Aeration reaches a high develop- ment in amphibious and floating forms, but air-passages are normally absent from submerged forms except as vestiges. Photosynthesis is marked in the former, but c
. Research methods in ecology. Plant ecology. 128 THE PLANT stantly below the water; in amphibious ones, they grow normally in the air. Floating plants have leaves in which the upper surface is in contact with the air, and the lower in contact with the water. Transpiration is at a maximum in the amphibious plant; it is reduced by half in the floating type, and is altogether absent in submerged plants. Aeration reaches a high develop- ment in amphibious and floating forms, but air-passages are normally absent from submerged forms except as vestiges. Photosynthesis is marked in the former, but considerably weakened in the latter. The vascular system, which attains a moderate developrhent in the amphibious type, is considerably reduced in floating forms, and it is little more than vestigiate in submerged ones. I. The amphibious type. Plants of this type grow in wet soil or in shallow water. The leaves are usually large and en- tire, the stem well developed, and the roots numerous and spread- ing. In the majority of cases the leaves are constantly above the water, but in some species the lower leaves are often covered, normally, or by a rise in level, and they take the form or struc- ture of submerged leaves. This is illustrated by Callitriche auttim- nalis, Hippiiris vulgaris, Ranun- culus delphinifalius, Proserpinaca palustris, Roripa americana, etc. The epidermis has a thin cuticle, or none at all, and is destitute of hairs. The stomata are numer- ous and usually more abundant The palisade tissue is represented. Fig. 37. Floating leaf of Spar^anium angus- tifolium. X 130. on the upper than on the lower surface by one or more well-developed rows, but this portion of the leaf is regularly thinner than that of the sponge part. The latter contains. large air-pas- sages, or, in the majority of cases, numerous air-chambers, usually provided with diaphragms. i"he stems are often palisaded, and are characterized by longitudinal air-chambers crossed by frequent diaphragm
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectplantec, bookyear1905
