FERNS. 



[ 261 ] 



FERNS. 



(annulus or connecticule), which causes the 

 bursting of the sac when ripe. In the Poly 

 podiaceae the annulus starts from the stalk 

 of the capsule (fig. 229) ; in Hymenophyllum 



Fig. 229. 



Marginaria verrucosa. 

 Thecae. Magnified 25 diameters. 



and Trichomanes it runs round in an oblique 

 line (like the ecliptic line on the globe) ; in 

 Gleichenia it is also oblique (fig. 235), 

 and in Schiz&a and Aneimia (fig. 12. p. 34), 



Fig. 230. 



Fig. 231, 



Fig. 232. Fig. 233. Fig. 234. 



Ceratopteris thalictroides. 



Fig. 230. Theca. Magn. 50 diams. 



Fig. 231. Do., bursting. Do. 



Fig. 232-4. Spores. Magn. 150 diams. 



Fig. 235. 



Gleichenia. 

 A theca. Magnified 40 diams. 



&c. it forms a kind of cap on the summit of 

 the case. 



These membranous sporanges a"re 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 reti- 

 culations (figs.232-4,236-9). (See SPORES.) 



Fig. 236. 



Fig. 237. 



Fig. 239. 



O O 



Spores of Ferns. 



Fig. 236. Aneimia asplenifolia. 



Fig. 237. Polypodium aureum. 



Fig. 238. Cystopteris fragilis. 



Fig. 239. Pteris longifolia. 



Magnified 100 diameters. 



The reproduction of the Ferns by their 

 spores exhibits some very remarkable phae- 

 nomena. When the spores are sown, they 

 germinate after a time by a protrusion of 

 the inner coat as a delicate membranous 

 pouch (fig. 240), which elongates and be- 

 comes divided by septa into an articulated 

 cellular filament ; some of the cells emit 

 slender tubular filaments (which are not cut 

 off by septa), apparently radical hairs, and 

 while these remain uncoloured, the larger 

 cells from which they arise acquire chloro- 

 phyll-granules. The young prothallium, 

 as it is called, increases in size by cell- 

 division, and at length acquires a somewhat 

 heart-shaped form (figs. 241-3), and soon 

 some of its cells produce, upon the under 

 surface, the structures called antheridia, 

 which consist of stalked cellular bodies, of 

 simple but peculiar structure, in the interior 

 of which are developed minute cellules con- 

 taining ciliated spiral filaments (spermato- 

 zoids), which, on the bursting of the anthe- 

 ridial sac, 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. 32. fig. 34). 



These antherids are often formed in large 

 numbers, and the prothallium goes on pro- 

 ducing them as long as it exists ; but at a 

 period somewhat later than the earlier an- 

 therids, there appear near the middle, at the 

 front of the under surface of the prothallium, 



