. Carnegie Institution of Washington publication. THE YOUNG SPOROPHYTE 155 that the leaves arise from the segments of the apical cell of the stem, and their tissues are therefore indirectly derived from the stem apex, we may say that the stem apex takes no part in the differentiation of the nbro-vascular system, which in the young sporophyte is composed entirely of the leaf and root traces. THE ROOT. Only a small number of sections of the primary root were obtained in Marattia Jouglasii, and these showed some variation, so that it is not possible to state posi- tively what is the typical form
. Carnegie Institution of Washington publication. THE YOUNG SPOROPHYTE 155 that the leaves arise from the segments of the apical cell of the stem, and their tissues are therefore indirectly derived from the stem apex, we may say that the stem apex takes no part in the differentiation of the nbro-vascular system, which in the young sporophyte is composed entirely of the leaf and root traces. THE ROOT. Only a small number of sections of the primary root were obtained in Marattia Jouglasii, and these showed some variation, so that it is not possible to state posi- tively what is the typical form of its apical cell, but there is no question that the primary root grows from a single initial cell, as in the other genera. In longitudinal section it appears oblong, with a broadly truncate base from which segments arise, as well as from the lateral faces. There seem to be regularly four sets of lateral cot. Fig. i A. Nearly median section of a young sporophyte of Danga jamaicensis, passing thruugh stem apex. X about 40. B. Another section of same, passing through second leaf, I2 C. Section of another^ similar sporophyte cut at right angles to that shown in A and B, and showing continuity of bundles of cotyledon and primary root, pr, gametophyte; tc, scales. segments, although cross-sections of the apical cell sometimes appear almost trian- gular. The root cap is formed in part from segments derived from the outer face of the apical cell, in part from similar segments cut off from the outer portion of the youngest lateral segments of the apical cell. The central cylinder of the root is formed in part from the basal segments of the apical cell, but the lateral seg- ments also contribute to it (fig. 141, D). In Angiopteris (fig. in, C) the apical cell in the earlier stages of the root may appear triangular in longitudinal section, but in the later stages it is usually more or less truncate. The primary root in Kaulfussia, in the few cases where satisfactory sections were made o
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