SECT. I 



CRYPTOGAMS 



449 



x 



genera. The sori of Scolopendrium are linear, and covered with a lip-shaped 



indusium consisting of one cell-layer They are so disposed in pairs, on different 



sides of every two successive nerves, that they appear to have a double indusium 



opening in the middle. In the genus Aspidium, 



on the other hand, each sorus is orbicular in form 



and covered by a peltate or reniform indusium 



attached to the apex of the placenta ; a glandular 



hair is frequently present on the stalk of the 



sporangium. The sori of Polypodium vulgare are 



also orbicular, but they have no indusia. In the 



common Bracken, Pteris aquilina, the sporangia 



form a continuous line along the entire margin 



of the leaf, which folds over and covers them 



with a false indusium. 



Besides the Polypodiaceae the Ferns include 



other families, mainly represented in the tropics, 



the sporangia of which differ in the construction 



of the annulus and in the mechanism of their 



dehiscence ( 11J ). The sporangia of the Cyatheacae, 



to which family belong principally the tree-like 



Ferns, are characterised by a complete annulus 



extending obliquely over the apex of the capsule 



(Fig. 409 B, 0). The Hymenophyllaceae, often 



growing as epiphytes on Tree-Ferns, have also 



sporangia, with a complete, oblique, or horizontal 



annulus. The sporangia of the Schizaeaceae, on 



theother hand, have an apical annulus ( Fig. 409 Z>), 



while in the Osmundaceae, of which the Royal 



Fern, Osmunda regalis, is a familiar example, 



the annulus is represented merely by a group of thick-walled cells just below the 



apex of the sporangium (Fig. 409 E). 



All the members of the Filices are homospor- 

 ous. The PROTHALLIUM has usually the form 

 of a flat, heart-shaped thallus (Fig. 399), bearing 

 the antheridia and archegonia on the under side. 

 In certain Hymenophyllaceae (Trichomanes) the 

 prothallium is filiform and branched, resembling 

 in structure the protonema of the Mosses, and 

 producing the antheridia and archegonia on 

 lateral branches (Fig. 410). 



The ANTHERIUIA and ARCHEGONIA ( 112 ) are 

 similarly constructed in nearly all Leptosporangi- 

 atae, and present differences from those of the 

 Eusporangiate Ferns ; those of Polypodium 

 vulgare (Figs. 411, 412) may serve as a type. 

 The antheridia are spherical projecting bodies 

 (Fig. 411 A, p), arising on young prothallia by 

 the septation and further division of papilla-like 

 protrusions from single superficial cells. When 

 mature, each antheridium consists of a central 



cellular cavity, filled with spermatozoid mother-cells, and enclosed by a wall formed 



2 G 



i. 410. Trichomanes rigidum. Por- 

 tion of a prothallus with an arche- 

 yoniophore (-4) to which a young 

 plant is still attached. (After 



GOEBEL.) 



Fiti. 411. Polypodium vulgare. A, 

 Mature, B, discharged antheridium ; 

 p, prothallium cell ; 1 and 2, ring- 

 shaped cells ; 3, lid-cell ; ' . />. 

 sperinatozoids. (A, B x 240 ; C, 

 D x 540.) 



