. Carnegie Institution of Washington publication. 138 I III HALES sections this is somewhat wedge-shaped, the narrow end turned outward and the broad base below. In cross-section this cell is nearly square in shape (rig. 107, A,x) and there may be seen a fairly regular series of four segments cut from the lateral faces. From the broad truncate base of the cell, segments are also cut off which contribute to the inner tissue of the stem.* Much the greater part of the epibasal meristem contributes to the cotyledon, which is soon evident as a broadly conical protuberance, somewhat flattened
. Carnegie Institution of Washington publication. 138 I III HALES sections this is somewhat wedge-shaped, the narrow end turned outward and the broad base below. In cross-section this cell is nearly square in shape (rig. 107, A,x) and there may be seen a fairly regular series of four segments cut from the lateral faces. From the broad truncate base of the cell, segments are also cut off which contribute to the inner tissue of the stem.* Much the greater part of the epibasal meristem contributes to the cotyledon, which is soon evident as a broadly conical protuberance, somewhat flattened on the side adjacent to the stem apex and merging gradually on the outer side into the large- celled tissue which adjoins the foot. To judge from the limited number of young embryos which I could examine, it seems that the growth of the cotyledon is not due to the activity of a single apical cell, but this point was somewhat uncertain. By the time that the cotyledon is established, growth has progressed in the young root, which now is seen to have a conspicuous apical cell, which divides rapidly so that the root quickly elongates in a direction opposite to that of the cotyledon (tig. 108). The apical cell of the primary root in M. doiiglam is not triangular in outline, but more or less quadrilateral, whether seen in longitudinal or cross sections (fig. 107, B). In form and segmentation it perhaps more nearly resembles that of Dancea than it does the tetrahedral apical cell which occurs in the young primary root oi'Angiopteris. Active cell divisions take place also in the tissue of the foot, which completely incloses the young root and becomes practically merged with it, so that it is quite impossible to say, at the time the root emerges, just how much of the tissue of its outer portion really belongs to the root itself and how much is derived from the original tissue of the foot. The latter is now no longer recognizable as such, the young sporophyte apparently at this time bei
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Keywords: ., bookauthorcarnegie, bookcentury1900, bookdecade1910, bookyear1911
