ON GENERA AND SPECIES. ay 
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 Gleichenia. They are either seated on 
the margin (marginal) or near or close to the costa (costal), 
or on or about the middle of the dise (medial) Whena 
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 laciniæ, or in regular rows, or con- 
 *inuous 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. 
sa 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 Acrostichew, 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. 
