302 ANTHERIDIA AND ARCHEGONIA 



Bryophyta, and are produced by the outgrowth of single surface- 

 cells. They are situated on the lower surface, and both kinds 

 usually occur on the same prothallus (Fig. 167). The antheridia 

 (an.), found mainly on the thinner marginal wings and the less 

 robust prothalli, are almost spherical structures (Fig. 168, g.) 

 with a small number of relatively large spermatozoid mother- 

 cells (s.). The enveloping wall (w.) is peculiar in being composed 

 only of two superposed ring-shaped cells surmounted by a 

 dome-shaped cap-cell (Fig. 168, e). The spermatozoids (Fig. 

 168, d), which are developed in the same way as in the Bryophyta 

 (cf. p. 277), have a spirally coiled, spindle-shaped body bearing 

 numerous cilia near the pointed end. Dehiscence of the an- 

 theridium, by the breaking away or rupture of the cap-cell 

 (Fig. 168, e and /), takes place in wet weather, and the liberated 

 spermatozoids swim in the film of water retained by capillarity 

 between the lower surface of the prothallus and the soil. 



The archegonia are restricted to the region of the cushion, 

 in which they are partially embedded, the necks alone projecting 

 (Fig. 167, ar. ; Fig. 168, a and b). The necks are all curved 

 towards the pointed end of the prothallus, and differ from those 

 of a Bryophyte archegonium in being short and composed of 

 only four longitudinal rows of cells (Fig. 168, c), whilst there 

 is but a single canal cell. The venter, containing the egg (o.) 

 and the ventral canal cell (v.c.), appears as a mere cavity in the 

 tissue of the prothallus. At maturity (Fig. 168, b) the four cells 

 at the top of the neck are forced apart by a mucilage containing 

 malic acid, formed during the disorganisation of the canal cells, 

 and an open passage is thus left leading down to the egg. It 

 is apparently the malic acid that attracts the spermatozoids to 

 the archegonia. 



After fertilisation the ovum becomes enveloped by a thin 

 membrane, and divides by three successive walls into octants 

 of a sphere (Fig. 169, A). Their further segmentation leads to 

 the differentiation of four apical cells, which are situated one 

 in each quadrant, and which respectively give rise to the root, 

 the stem, the first leaf, and the " foot " of the embryo. The 

 foot develops as a large parenchymatous sucker which becomes 

 firmly lodged in the tissue of the cushion, from whose cells it 

 absorbs nourishment for the young Fern (Fig. 169, B, /). 



