CRYPTOGAMS 



405 



and sterile segments. In Ophioglossum the sterile leaf-like segment is tongue- 

 shaped, the fertile segment narrow and cylindrical, bearing the sporangia in two 

 rows sunk in the tissue. The sterile portion of the leaf of 

 Botrychium is pinnate, while the fertile segment is pin- 

 nately branched, and thickly beset on the inner side with 

 large nearly spherical sporangia. 



All the members of the Filices axe homosporous. 

 The prothallium has usually the form of a flat, 

 heart-shaped thallus (Fig. 330), bearing the anther- 

 idia and archegonia on the under side ; but in 

 Botrychium it is represented, on the contrary, by a 

 small subterranean tuberous body which is sapro- 

 phytic, and produces the sexual organs on the 

 upper side. In certain Hymenophyllaceae (Tri- 

 chomanes), on the other hand, the prothallium is 

 filiform and branched, resembling in structure the 

 protonema of the Mosses, and producing the 

 antheridia and archegonia on lateral branches. 



The antheridia and archegonia are similarly 

 constructed in nearly all Ferns; those of Poly-, 

 podium vulgare (Figs. 338, 339) may serve as a 

 type. The antheridia are spherical projecting 

 bodies (Fig. 338, A, p), arising on young pro- 

 thallia by the septation and further division of 

 papillse-like protrusions from single superficial 



cells. When mature, 



-Botrychium Lun- 

 (£ nat. size.) 



- Polypodium vulgare. 



each antheridium 

 consists of a central 

 cellular cavity, filled 

 with spermatozoid 

 mother-cells, and en- Fi 

 closed by a wall 

 formed of two ring- 

 shaped cells (A, 1, 2) and a lid-cell (3). 

 The spermatozoid mother-cells are pro- 

 duced by the division of the central cells. 

 They are discharged from the antheridium 

 by the pressure exerted by the swollen 

 ring -cells, and the consequent rupturing 

 of the lid -cell. Each mother -cell thus 



Mature, S, discharged antheri- 

 dium ; p, prothallium cell ; 1 aDd 

 2, ring-shaped cells ; 3, lid-cell ; C, 



spermatozoid in motion ; d, one ejected liberates a spirally coiled sperma- 

 W> & tozoid. The anterior extremity of the 

 spermatozoid is beset with numerous 

 cilia, while attached to its posterior end is a small vesicle which con- 

 tains a number of granules, and represents the unused remnant of 

 the contents of the mother-cell (Fig. 338, D, C ; Fig. 70, B, p. 67). 



fixed with iodine solution, 

 x 240 ; C, D x 540.) 



