FERNS. 



[ 321 J 



FERNS. 



Trichomanes it runs round in an oblique line 

 (like the ecliptic line on a globe) ; in Glei- 

 chenia it is also oblique (fig. 231) ; and in 

 Schizcea and Aneimia (fig. 12, p. 41) &c. 

 it forms a kind of cap on the summit of the 

 case. 



Fig. 228. Fig. 229. Fig. 230. 



Ceratopteris thalictroides. 

 Figs. 228-230. Spores. Magn. 150 diams. 



Fig. 231. 



Grleichenia.- 

 A theca. Magnified 40 diams. 



^ membranous sporangia are filled 



with spores having a double coat, like pol- 

 len-grains ; and, as in these, the outer coat 

 is ordinarily coloured, and either smoothish 

 or marked with points, streaks, ridges, or 

 reticulations (figs. 228-230, 232-235). (See 

 SPOKES.) 



Fig. 232. 



Fig. 233. 



Fig. 234. 



Fig. 235. 



Spores of Ferns. 



Fig. 232. Aneimia asplenifolia. 

 Fig. 233. Polypodium aureum. 

 Fig. 234. Cystopteris fragilis. 

 Fig. 235. Pteris longifolia. 



Magnified 100 diameters. 



The reproduction of the Ferns by their 

 spores exhibits some very remarkable phe- 

 nomena. When the spores are sown, they 

 germinate after a time by a protrusion of 

 the inner coat as a delicate membranous 

 pouch (fig. 236), which elongates and be- 

 comes divided by septa into an articulated 

 cellular filament ; some of the cells emit 

 slender tubular, not septate, filaments, form- 

 ing radical hairs; and while these remain 

 imcoloured, the larger cells from which they 



Fig. 236. 



Fig. 237. 



Fig. 238. 



Fig. 239. 



Germination of Pteris longifolia. Magn. 100 diams. 



arise acquire chlorophyll-granules. The 

 young prothallium, as it is called, increases 

 in size by cell-division, and at length ac- 

 quires somewhat the form of a heart (figs. 

 236-239). Some of its cells produce, upon the 

 margin or the under surface, the trichonia- 

 tous structure! called antheridia ; which con- 

 sist of stalked cellular bodies, of simple but 

 peculiar structure, in the interior of which 

 are developed minute cellules containing 

 ciliated spiral filaments, the spermatozoids. 

 These are corkscrew-shaped, with 3 or 4 



coils, and the front end finely ciliated. 

 On the bursting of the antheridial sac, 

 they escape, not only from this, but from 

 their own parent-cells, and swim about 

 actively in the water by the aid of their 

 vibratile cilia (PI. 40. fig. 34). 



The antheridia are often formed in large 

 numbers, and the prothallium goes on pro- 

 ducing them as long as it exists j but at a 

 period somewhat later than that of the 

 earlier antheridia, there appear near the 

 middle, at the front of the under surface of 



