20 
HISTORY OF BRITISH FERNS. 
great abundance of seed-like bodies, which are technically 
called spores, and are contained in little cases of very sin- 
gular construction. Collectively, these cases and their 
contents are called the fructification. The seed-cases, as 
already remarked, are attached in the different species to 
certain determinate thickened portions of the veins, which 
points of attachment are called the receptacles. Each 
separate mass or cluster of the seed-cases is called a sorus, 
but as they are generally spoken of collectively, the plural 
term sori becomes much more frequently used. The sori 
are marginal when they grow out from the margin, and 
dorsal when they occupy some part of the under surface of 
the frond. 
The seed-cases — called also spore-cases, or sporangia, or 
thecoe — are mostly minute roundish-oval bodies, containing 
one cavity, and nearly surrounded by a jointed vertical 
band called a ring, which is continued from the base so as 
to form a short stalk, by which they are attached. When 
they have reached maturity, the elasticity of the ring bursts 
the case by an irregular transverse fissure, and the seeds 
or spores, in the shape of fine dust, almost invisible, become 
dispersed. This is what occurs in the majority of the native 
species. In Trichomanes and Hymenophyllum, however, 
