FRUCTIFICATION IN FERNS. 



II 



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 son', and may be naked, as in Polypodium, or 

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

 Aspidium (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 POLYPODIACE^ 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 .Fio.2. Sporan- 



, . , . , ,. gium of Polypo- 



roundish, oblong, or linear in shape, or arranged dium vuigare, L. t 

 in variously forking lines, or may even be spread spm-es^'Kchen- 

 in a stratum over the entire under surface of the lar & ed - 

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

 tachment. 



28. In the other sub- 

 orders of FILICES the spo- 

 rangia are variously ar- 

 ranged. In the HYMENO- 

 PHYLLACE/E or filmy ferns 

 the flattened sporangia are 

 sessile along a filiform recep- 

 tacle, and are surrounded 

 with a complete transverse 

 annulus. At maturity they 

 open vertically (Fig. 3). In 



FIG. 



FIG. 



Much enlarged. 

 the SCHIZ^EACE^E 



fpta 



the 



sporangia 



