. The structure and development of mosses and ferns (Archegoniatae). Plant morphology; Mosses; Ferns. 24» MOSSES AND FERNS CHAP. posed of several layers of cells, and this encloses a cavity in which are the growing point of the stem and the youngest leaf. The leaves here form much more rapidly than in the species of the temperate regions, as the growth continues uninterruptedly throughout the year. The real apex of the stem forms an in- clined nearly plane surface, slightly raised in the centre, where the single apical cell is placed (,A,B). This cell is by no means conspicuous, and not
. The structure and development of mosses and ferns (Archegoniatae). Plant morphology; Mosses; Ferns. 24» MOSSES AND FERNS CHAP. posed of several layers of cells, and this encloses a cavity in which are the growing point of the stem and the youngest leaf. The leaves here form much more rapidly than in the species of the temperate regions, as the growth continues uninterruptedly throughout the year. The real apex of the stem forms an in- clined nearly plane surface, slightly raised in the centre, where the single apical cell is placed (,A,B). This cell is by no means conspicuous, and not always readily found, but probably is always present. It has the form of an inverted three-sided pyramid, but the lateral faces are more or less strongly convex, and the apex may be truncate. From the few cases observed it is not possible to say whether in addition to the three sets of lateral segments basal seg- ments are also formed, but it is by no means impossible that such is the case. Ac- cording to investigations of Rostowzew ((I), p. 451), the apical cell of the stem of Ophioglossum vulgatum shows considerable variation, and may be either a three or four-sided prism, i. e., it ap- parently also may have the base truncate. Holle's (i) description agrees y^rith this except that he states that he always found the cell pointed below, not truncate. The segments cut off from the lateral faces are large, and the divisions irregular. They are appar- ently formed in very slow succession, and the irregularity of the succeeding divisions in the segments themselves soon makes it impossible to trace their limits. Each segment apparently gives rise to a leaf, but this is impossible to determine with certainty. The first wall in the young segment probably divides it into an inner and outer cell, but the next divisions could not be deter-. FiG. 133.—ophioglossum pendulum. A, Me- dian longitudinal section of stem apex, X4: X, the growing point; B, young sporophyll, X2; sp, the spora
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