PTERIDOPHYTA. 207 



The ARCHEGONIA have been already mentioned (p. 199, Fig. 201). 

 The ANTHERIDIA are hemispherical or slightly conical bodies (Fig. 

 206). They consist, as in the Mosses, of a wall formed by one 

 layer of cells, which encloses a number of spermatozoid-mother- 

 cells (A and B). The antheridia when ripe absorb water, and 

 are ruptured, and the spirally-coiled spermatozoids liberated (Fig. 

 206 S). The spermatozoids have been observed to pass down the 

 neck of the archegonium, and to fuse with the oosphere. 



The asexual generation. The first leaf, the "cotyledon," 

 of the embryo developed from the oospore (Figs. 202, 205) is 

 always small, and has a very simple shape. The leaves which 

 occur later become more perfect, stage by stage, until the perma- 

 nent form of leaf has been attained. The STEM is most frequently 

 a subterranean or a semi-aerial rhizome ; it is only in the tropical, 

 palm-like Tree-Ferns, that the stem raises itself high in the air and 

 resembles that of a tree, with leaf-scars or with the remains of 

 leaves attached (Figs. 207, 203) ; in certain species the stem is en- 

 cased in a thick mat of aerial roots (Dicksonia antarctica). When 

 the rhizome is horizontal the internodes are frequently elongated, 

 and the leaves are arranged in two rows, as in Poly podium vulgare 

 and in the Bracken-Fern (Pteridium aquilinum), etc. ; it is also 

 generally dorsiventral, having a dorsal side on which the leaves are 

 situated, and a ventral side, different from the former, on which 

 the roots are borne. When the stem ascends iu an oblique direc- 

 tion, or is nearly vertical, its internodes are extremely short, and 

 the leaves are arranged in a spiral line with a complicated phyllo- 

 taxis, e.g. in Atliyrium filix-fceniina, Asyidium jilix-mas, etc. The 

 BRANCHING upon the whole is extremely slight, and is generally 

 confined to the petiole (e.g. Aspid. filix-mas), or to the stem near 

 the insertion of the leaves. Several species normally form buds on 

 different parts of the lamina. The buds which are formed on the 

 stem are not confined to the leaf -axil as in the higher plants. 

 The Tree-Ferns, generally, do not branch at all. 



The VASCULAR BUNDLES are concentric, with the wood surrounded 

 by the soft bast. In tranverse section they are seen as circles or 

 irregularly-shaped figures (Fig. 203), the name of " King Charles 

 and the Oak" (Bracken-Fern) having originated from the appear- 

 ance which the bundles present in oblique section. In Osmunda 

 they are collateral and resemble those of the Flowering-plants. 

 Round each individual bundle is often a sheath of thick- walled, 

 hard, brown, sclerenchymatous cells, which act as a mechanical 



