FRUCTIFICATION IN FERNS. 



n 



of flowering plants. These spores are collected in little sacs 

 known as sporangia or spore cases. The sporangia in the true 

 ferns (POLYPODIACE.E) are collected in little clusters on the 

 back of the frond, or are variously arranged in lines along the 

 veins or around the margins (Fig. i). These clusters of spo- 

 rangia are called sori, and may be naked, as in Polypodium, or 

 provided with a special covering known as the indusium, as in 

 Dryopteris (Fig. 8). The various forms of the 

 sori and indusia serve as the basis for classifica- 

 tion into genera and tribes, while each sub-order 

 has its peculiar form of sporangia. 



27. In the PoLYPODlACEyE the sporangia 

 are more or less completely surrounded with a 

 jointed vertical ring or annulus, and at maturity 

 burst open transversely by the straightening of 

 the annulus and discharge their copious spores 

 (Fig. 2). The clusters of sporangia are said to 

 be marginal, intramarginal, or dorsal, according 

 as they have their position at the margin or 

 more or less remote from it. They may be .F1G.2.— Sporan- 



,. , , , ,. . , ■' ' , Slum of Polypo- 



roundish, oblong, or linear m shape, or arranged dium vuigare, L., 

 in variously forking lines, or may even be spread spores'^'ji^ch'en- 

 in a stratum over the entire under surface of the ''"'ged. 

 frond. They are called indusiate or non-indusiate according as 

 they are covered or naked ; and the indusia may be inferior (at- 

 tached below the sorus), as in Woodsia (Fig. 9), or superior, as 

 in Dryopteris (Fig. 8), or of various intermediate methods of at- 

 tachment. 



28. In the other families 

 of Filicales the sporangia 

 are variously arranged. In 

 the Hymenophyllace^ or 

 filmy ferns the flattened spo- 

 rangia are sessile along a 

 filiform receptacle, and are 

 surrounded with a complete 

 transverse annulus. At ma- 

 turity they open vertically 

 (Fig. 3). In the SchiZjEACE^ the sporangia are ovate, sur- 



Fig. 3. Fig. 4. 



Figf. 3. — Enlarged sessile sporangium 

 of Trickomanes radicans Swz. 



Figr- 4- — Sporangium of Schizeea pu- 

 silla Pursh, showing the apical ring. 

 Much enlarged. 



