The structure & development of the mosses and ferns (Archegoniatae) . ng at a later stage. After this has begun to form, itsgrowth is very rapid, and it soon overtakes the archegoniumand grows beyond it, and finally forms a vesicular body,plainly visible to the naked eye, at the bottom of which thearchegonium lies. The formation of this involucre is quiteindependent of the fertilisation of the archegonium, and asthese peculiar vesicles cover completely the whole dorsal 76 MOSSES AND FERNS CHAP. surface of the plant, they give it a most characteristicappearance. Usually each archegonium has its
The structure & development of the mosses and ferns (Archegoniatae) . ng at a later stage. After this has begun to form, itsgrowth is very rapid, and it soon overtakes the archegoniumand grows beyond it, and finally forms a vesicular body,plainly visible to the naked eye, at the bottom of which thearchegonium lies. The formation of this involucre is quiteindependent of the fertilisation of the archegonium, and asthese peculiar vesicles cover completely the whole dorsal 76 MOSSES AND FERNS CHAP. surface of the plant, they give it a most characteristicappearance. Usually each archegonium has its own envelope,but Leitgeb ^ states that two or even more may be surroundedby a common envelope. When ripe, the venter of the arche-gonium is somewhat enlarged, but not so much as in egg-cell is very large, oval in form, and nearly fills thecavity of the single-layered venter. The first wall in the embryo is transverse, and divides theegg cell, which before division becomes decidedly elongated,into two nearly equal cells. Ordinarily in each of these cells. Fig. 29.—Sphcerocarpus ter7-cstris var. Californicus (Aust.). Development of the , Longitudinal sections, x6oo; D, X300. similar transverse walls are formed before any vertical wallsappear, so that the embryo consists of a simple row of in the Marchantiacese the first wall separates the futurecapsule from the stalk, and in this respect SpJicEvocarpusapproaches the Marchantiaceae rather than the Junger-manniacese. Following the transverse walls there are formedin all the upper cells nearly median vertical ones, which areintersected by similar ones at right angles to. them, so that inmost cases (although this is not absolutely constant) the upper ?* Leitgeb (7), vol. iv. p. 68. IV THE JUNGERMANNIACE^ 77 half of the young sporogonium at this stage (Fig. 30, A)consists of two tiers, each consisting of four cells. The lowerpart of the embryo is pointed, and the basal cell either under-
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