ON GENERA AND SPECIES. 17 



dependent upon the form of the receptacles, which are 

 their foundations. Thus, when the receptacles consist of a 

 point only, the sori are always round, termed punctiform 

 while linear receptacles bear sori of various forms, being 

 oblong, elliptical, or linear, either simple, straight, or arcuate, 

 forked or reticulated. 



The sporangia of each sorus are generally crowded, or, 

 in some cases, few, being side by side on the receptacle, as 

 in Ceratopteris and Gleiclienia. They are either seated on 

 the margin (marginal) or near or close to the costa (costal), 

 or on or about the middle of the disc (medial). When a 

 little within the margin they are termed ante-marginal. 

 In some they are in pedicellate dents, exserted on the 

 margin. They are irregularly scattered over the surface 

 or solitary in multifid lacinise, or in regular rows, or con- 

 tinuous lines (serial). When the lines diverge at an angle 

 from the mid-rib they are said to be oblique, and when 

 parallel with either the margin or the costa, transverse. 



For their position on the veins the same terms are used 

 as those given for the receptacle. 



As a general rule, each sorus is distinct and well defined, 

 but in many cases the receptacles are so very close together 

 that the sporangium of one sorus runs into that of the con- 

 tiguous one (confluent), and thus normally punctiform sori 

 become oblong or linear. In the tribe Acrostichece, in which 

 the fertile fronds are contracted, the sori have no definite 

 form, the sporangia occupying the whole of the under 

 surface or in patches. They are borne on one side of con- 

 tracted spikes, or on simple or compound racemes, as in 

 Schizcea, Lygodium, Anemia, and Osmunda. 



