. The structure and development of mosses and ferns (Archegoniatae). tube. end of the germ-tube is composed of eight nearly equal cells oroctants. As these divisions proceed the oil drops which are soabundant in the undivided germ-tube disappear almost com-pletely, and are doubtless used up by the growing cells. According to Leitgebs view, and that of other authors, theeight-celled body at the end of the germ-tube is a sort of pro-tonema, from which the gametophore arises as a lateral out-growth. I have seen nothing in the species under considerationwhich supports such a view. Here the axis of
. The structure and development of mosses and ferns (Archegoniatae). tube. end of the germ-tube is composed of eight nearly equal cells oroctants. As these divisions proceed the oil drops which are soabundant in the undivided germ-tube disappear almost com-pletely, and are doubtless used up by the growing cells. According to Leitgebs view, and that of other authors, theeight-celled body at the end of the germ-tube is a sort of pro-tonema, from which the gametophore arises as a lateral out-growth. I have seen nothing in the species under considerationwhich supports such a view. Here the axis of growth is con-tinuous with that of the germ-tube, and in some cases at least, 38 MOSSES AND FERNS CHAP. and probably always, a single apical cell is developed at theapex at a very early stage. Probably this initial ^ell is one ofthe four terminal octant cells resulting from the first cell sometimes has but two sets of segments cut off fromit at first, alternately right and left, but whether this form isconstant in the young plant I cannot now Fig. g.—Riccia trichocarpa. Later stages of germination. A, from below, X260;B, optical section of A, showing apical cell x, XS2o; C, X85; r, rhizoids. Inter-cellular spaces have begun to develop. The four lower quadrants also divide, at first only bytransverse walls, and these cells lengthening give rise to acylindrical body composed of four rows of cells, terminated bythe more actively dividing group of cells at the summit. Thesingle apical cell is soon replaced by the group of initials foundin the full-grown gametophyte, and the method of growth from II MUSCINE^—HEPA TICAL—MARCH ANT I ALES 39 now on is essentially the same. The growth of the cells in theforward part of the dorsal surface of the young thallus is moreactive than that of the ventral side, so that they project overthe growing point (Fig. 9), and as the outer cells of the lateralsegments of the apical cell (or cells) also increase rapidly insize a
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