I. FILICES. 899 



BEPRODUCTIVE ORGANS composed of capsules (sporangia). SPORANGIA springing 

 from the nerves, on the lower surface or near the margin of the fronds, and collected 

 in groups (sori). SORT naked, or covered either with a fold of the margin of the frond, 

 or with a prolongation of the epidermis (indusium) . Sometimes their abundance in- 

 duces the atrophy and more or less complete disappearance of the leaf-like blade of 

 the frond, and they then form panicles or spikes isolated at the end of the general 

 frond (Osmunda, Aneimia, Lygodium, &c.). Each sporangium is pedicelled or sessile, 

 variously dehiscent, and usually furnished with a variously shaped elastic ring ; the 

 sporangium contains numerous free reproductive spherical or angular corpuscules 

 (spores), with a smooth warted or reticulate surface. These spores were originally 

 enclosed by fours in cells, which afterwards decay. Under the influence of humidity 

 [rather of drought] the sporangium opens or bursts, and the spores are elastically 

 expelled. 



The spores when placed on damp earth at once begin to germinate by emitting 

 a filament which develops into a small foliaceous cellular expansion, emarginate at 

 the tip (proembryo, prothallus). On the lower surface of the prothallus are soon 

 developed small cellular protuberances, usually resulting from the superposition 

 of three cells, of which the lower acts as a support, and the upper as a cover to 

 the middle one ; this latter contains a mucilaginous tissue, the cells of which con- 

 tain flattened threads, coiled in a helix, furnished with a series of numerous short 

 cilia, accompanied by a small vesicle ; these moveable bodies have been termed 

 antherozoids, and the organ which contains them antheridia. 



In the vicinity of the antheridia appear, a little later, somewhat larger cellular 

 ovoid or rounded organs, terminated by a sort of style, which is open at the period 

 of fertilization. These cellular sacs, analogous to the ovules of Phanerogams, are 

 named archegonia ; at the bottom of their cavity is seen a globose utricle which 

 has been compared to the embryonic sac. In this utricle a vesicle soon appears 

 from which the new plant will be developed. 



All the conditions for fertilization being thus arranged, the antherozoids break 

 the wall of the antheridia, drawing after them the mucilaginous vesicles, and escape, 

 executing, by means of the vibratory hairs at one of their extremities, rapid move- 

 ments, which are assisted by the rain or dew which moistens the mucilage expelled 

 with them from the mother-cell. They thus reach the canal of the archegonium, 

 and fertilization is secured ; a small cellular mass is then developed in the fertilized 

 archegonium, which lengthens into an erect axis, on the top of which fronds will be 

 developed, and from the base lateral roots. The prothallus soon disappears. 



Some species, notably those which grow on rocks or on walls exposed to the 

 heat of the sun, and the fronds of which are fragile, have the power of reviving 

 after being almost entirely dried up. 



TRIBE I. POLTPODIACE^J. 



Elastic ring generally narrow, prolonged from one side of the rather long 

 pedicel, interrupted at the top or the opposite side near the pedicel. 



SM 2 



