. Nature and development of plants. Botany. 272 STRUCTURE OF RICCIOCARPUS or dichotomous branching of the thallus, so characteristic of these plants (Fig. 179, A, B). The appearance of many of these hepatics is suggestive of the algae. Especially is this true of the aquatic Ricciocarpus and Riccia. (a) Structure of Ricciocarpus.—^An examination of the struc- ture of one of these will show, however, that extensive changes have been induced in even the simplest forms. The new stimuli to which the terrestrial conditions expose them cause a remark- able series of transformations in the cells that
. Nature and development of plants. Botany. 272 STRUCTURE OF RICCIOCARPUS or dichotomous branching of the thallus, so characteristic of these plants (Fig. 179, A, B). The appearance of many of these hepatics is suggestive of the algae. Especially is this true of the aquatic Ricciocarpus and Riccia. (a) Structure of Ricciocarpus.—^An examination of the struc- ture of one of these will show, however, that extensive changes have been induced in even the simplest forms. The new stimuli to which the terrestrial conditions expose them cause a remark- able series of transformations in the cells that are cut off from the. c Fig. 179. Forms of semiaquatic Marchantiales: A, Riccia, showing the dichotomous branching of the thallus. B, Ricciocarpus. The sexual or- gans are concealed in furrows that appear as radiating lines in the center of the branches. C, diagram of a cross-section of a branch, showing the male gametangia in the bottom of one of the furrows. apical cell. The upper cells of the thallus, as soon as they are formed at the growing point, are exposed directly to the air and light, and they develop chlorophyll and grow up into vertical rows or plates just as you have already noticed in the palisade chlorenchyma of the leaf (Fig. 180, ^). At an early period these rows of green cells become separated so that air spaces arise between them, and thus the chlorophyll-bearing cells are brought into direct contact with the atmosphere and enabled to carry on photosynthesis to the best advantage. The terminal cells of these rows enlarge considerably and form a rudimentary epider- mis. It is also interesting to note that the direct contact of the cells with the atmosphere results for the first time in the forma-. 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 Curtis, Carlton Clarence, 1864-1945. New Yor
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