. The structure and development of mosses and ferns (Archegoniatae). early, it may develop amidrib extending nearly the wholelength of the prothallium; but usuallyit does not form until relatively basal segment of the initial cellsdivides into a dorsal and ventral cell(semi-segment), the latter the largerof the two, and with much moreactive growth. The latter alone isconcerned in the growth of the pro-jecting cushion. Each ventral semi-segment Is first divided by a w^all parallel with the primarysegment wall, and from the anterior of these cells, almostexactly as in Notothylas, the a
. The structure and development of mosses and ferns (Archegoniatae). early, it may develop amidrib extending nearly the wholelength of the prothallium; but usuallyit does not form until relatively basal segment of the initial cellsdivides into a dorsal and ventral cell(semi-segment), the latter the largerof the two, and with much moreactive growth. The latter alone isconcerned in the growth of the pro-jecting cushion. Each ventral semi-segment Is first divided by a w^all parallel with the primarysegment wall, and from the anterior of these cells, almostexactly as in Notothylas, the archegonium is developed. It isnot possible to make out any definite succession of walls bywhich the axial cell of the archegonium is cut out, but it soonis recognisable by the granular cytoplasm and large in Marattia, the first transverse wall separates the inner cellfrom the cap cell, and the inner one then divides into the basaland the central cells. The cover cell divides into the fourprimary neck cells, and the central cell arching up between these. Fig. 176.—Ripe archegonium ofO. struthiopteris in the actof opening, X300; 0, theegg. IX FILICINE^ LEPTOSPORANGIATJE 319 has the pointed apex cut off by a curved wall from the centralcell. The primary neck canal cell, so formed, is noticeablysmaller than that of Marattia. The neck cells, which in theeusporangiate forms all grow alike, here show a difference, andthe two anterior rows develop faster than the posterior ones, sothat these rows are longer and the neck is strongly bent back-ward. In Onoclea there are usually about seven cells in eachanterior row and about two less in the posterior ones. Theneck cells are almost colourless, with distinct nuclei, and a fewsmall, pale chloroplasts. From the central cell is now cut offthe ventral canal cell, which is quite small, and separated fromthe egg by a strongly concave wall. The nucleus of the neckcanal cell always divides, but no division w^all is formed, andthe two
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