362 



XXVI. REPRODUCTION OF THE PTERIDOPHYTA. 



embryo in the fertilised archegonia. The venter of the arche- 

 gonium has swollen, its outward-projecting wall has become 

 multilamellar ; above it stands the brown and shrivelled neck. 

 The embryo, now composed of a larger or smaller number of 

 cells, appears in its interior. At a later stage the wall of the 

 venter is ruptured, and the rudiment of the first leaf makes its 

 appearance from it. 



There still remains one thing to see the archegonia in section. 

 Median sections must be taken, as the archegonia are found only 

 on the middle line of the prothallium. In order to facilitate the 

 cutting, we lay together several prothallia, carefully arranged one 

 upon another, after we have previously removed all grains of 

 sand. We now readily find the desired structures on the sections. 



The archego- 

 nium, as we 

 have seen (Fig. 

 133, A and B), 

 has its ventral 

 portion sunk 

 in the prothal- 

 lium, the neck 

 being bent. 

 Neck canal- 

 cell (K r ) and 

 ventral canal- 

 cell (K") are 

 now distin- 

 guishable, as also the oosphere (o), together with its nucleus. 

 The ventral portion of the archegonium is covered by a layer 

 of flat cells. In a ripe, opened archegonium (B) a colourless spot 

 the receptive spot can often be noticed at the apex of the 

 oosphere, at which takes place the absorption of the spermato- 

 zoid. Less median sections may perhaps show us the antheridia, 

 also in profile. 



Development of the Prothallium. The raising of fern pro- 

 thallia from spores has many points of interest. Amongst the 

 quickest of all spores to germinate are those of the Eoyal Fern, 

 Osmunda regalis. The spores of the curious annual stove aquatic 

 fern, Ceratopteris thalictroides, are of special utility if obtainable, 

 owing to the transparency of the structures developed from them, 

 We can sow the spores on a piece of moderately soft tile, laid 



FIG. 133. Polypodium vulgare. A , unripe archegonium ; K ', 

 neck canal -cell ; K", ventral canal-cell ; o, oosphere ; B, ripe 

 opened archegonium (x 240). 



