FERNS. 



[ 321 J 



FERNS. 



Trichomanes it runs round in an oblique line 

 (like the ecliptic line on a frlobe) ; in Gloi- 

 cheiiia it is alst) oblique (tig. 231) ; and in 

 Scfiizcea and A^teimia (fig. 12, p. 41) &c. 

 it forms a kind of cap on the summit of the 

 case. 



229. 



Fifr. 230. 



Ceratopteris thalicfroides. 

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



Fig. 231. 



Gleichenia." 

 A theca. Magnified 40 diams. 



These 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 marlted with points, streaks, ridges, or 

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

 Spores.) 



Fig. 232. 



Fig. 234. 



Fig. 235. 



Spores of Ferns. 



Fig. 232. Aneimia asplenifolia. 

 Fig. 233. Polyijodium aiireum. 

 Fig. 234. Cystopteris fragilis. 

 Fig. 23.5. Pteris longifolia. 



Magnitied 100 diameters. 



The reproduction of the Ferns by tlieir 

 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. 



Fiff. 239. 



Grermination of Pteris longifolia. Magn. 100 diams. 



arise acquire chlorophyll-gTanules. The 

 joiing 2}rot/ialliiim, as it is called, increases 

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

 quires somewhat the form of a heart (figs. 

 2-36-239). Some of its cells produce, upon the 

 margin or the under sm-face, the trichoma- 

 tous structures called anther idia; which con- 

 sist of staUied cellular bodies, of simple but 

 peculiar structm-e, 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 tlie 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 (PL 40. fig". 34). 



The antheridia are often formed in large 

 numbers, and the prothallium goes on pro- 

 ducing them ns long as it exists; 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 



