Meristem in Osmunda cinnamomea

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Abstract
The rhizome in the sporeling stage grows by means of a tetra-hedral apical cell. As the plant reaches maturity the segmentation of the apical cell usually becomes progressively less regular until the identity of the original apical cell is lost, and growth takes place by 2 or more initials. Cells destined to become desmogen tissue may be recognized in the 2nd segment from the apical cell. Due to the slow growth of the rhizome and the frequency of leaf gaps, it is difficult if not impossible to refer any portion of the mature rhizome to any definite portion of the segments from the apical cell or group of initials. The pericycle and endodermis apparently have independent origins, although decisive evidence was lacking. The roots arise in tissue which later gives rise to the pericycle. The undifferentiated endodermis acts as a sort of protective layer to the young root. The number of cells of most young roots is increased for a time by means of an apical cell with 5 cutting faces. As in the stem, progressive irregularity in segmentation of this cell often results in the formation of 2 or more initial cells which replace the apical cell. The evidence obtained supports the conclusions of Bower that the Osmundaceae occupy an intermediate position between the leptosporangiate and the euspo-rangiate ferns, but it throws no light upon the relative antiquity of the 2 groups.

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