. The structure and development of mosses and ferns (Archegoniatae). the Polypodiaceae these occur moreor less plentifully, and are often the result of insufficient nutri-tion ; but in Onoclea it is something more than this, as not onlythe small prothallia are male, but the large ones are exclusivelyfemale, and not hermaphrodite, as in most Ferns. The Sex-Organs The first antheridia appear within three or four weeks underfavourable conditions, and are formed either from marginal orventral cells of the prothallium. The very young antheridiumis scarcely to be distinguished from a young rhizoid.
. The structure and development of mosses and ferns (Archegoniatae). the Polypodiaceae these occur moreor less plentifully, and are often the result of insufficient nutri-tion ; but in Onoclea it is something more than this, as not onlythe small prothallia are male, but the large ones are exclusivelyfemale, and not hermaphrodite, as in most Ferns. The Sex-Organs The first antheridia appear within three or four weeks underfavourable conditions, and are formed either from marginal orventral cells of the prothallium. The very young antheridiumis scarcely to be distinguished from a young rhizoid. Like it, IX FILICWEM LEPTOSPORANGIAT^ 315 it arises from a protrusion of the cell which is cut off by a wall,which is usually somewhat oblique. The papilla thus formedenlarges and soon becomes almost hemispherical. It containsa good deal of chlorophyll and a large central nucleus sur-rounded by dense cytoplasm. The first wall in the young an-theridium (Fig. 174, A) is very peculiar. It has usually theform of a funnel, whose upper rim is in contact with the wall of. Fig. 174.—Onoclea struthiopteris. Development of the antheridium. A-C, Verticalsection, X6oo; D, two nearly ripe sperm cells; E, free spermtatozoid, X about1200. the antheridium cell, and whose base strikes the basal wall ofthe antheridium. Sometimes this first wall does not reach to thebase, in which case it is simply more or less strongly concave,and the basal cell cut off by it from the antheridium is discoidinstead of ring-shaped (Fig. 174, B). The second wall ishemispherical, and is nearly concentric with the outer w^all ofthe antheridium. The dome-shaped central cell produces the 3i6 MOSSES AND FERNS CHAP. mother cells of the spermatozoids, and has much more densecontents than the outer cells, but all the chloroplasts remain inthe latter. A third wall now forms in the upper peripheralcell, much like the first one in form, and cuts off a cap cell atthe top. The young antheridium at this stage consists of fourc
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Keywords: ., bookauthorcampbelldouglashought, bookcentury1900, bookdecade1910
