DEFINITIONS. 
XI 
Is changed in texture, and closely occupied by the sporangia 
(amorphous). It is generally superficial, sometimes immersed in 
the substance of the frond, or considerably elevated, and then 
globose or columnar. 
The sporangia are transparent, globose, oval, or pyriform uni- 
locular cases, each girded by a more or less complete, elastic, ar- 
ticulated ring ; or destitute of a ring, then sometimes by combi- 
nation oblong, or linear, opaque, and multilocular, usually pedi- 
cellate, rarely sessile, produced in crowded masses (sori) on each 
receptacle ; rarely solitary or few, sometimes pilose, and a num- 
ber often abortive and deformed. 
The sori are collections of sporangia, and have the same form, 
position, and direction, as the receptacles ; therefore round , 
elongated , or amorphous , and seated on or close to the margin 
(of the frond or segment) ( marginal l), or between the margin and 
midrib ( intramarginal ), or close to the midrib ( costal ) ; when 
elongated they are either oblong or linear, constituting a con- 
tinuous or interrupted line, which forms more or less of an angle 
with the midrib (oblique), or runs parallel with the midrib or 
margin ( transverse ). They are either naked, or each sorus is fur- 
nished with a membranaceous covering of various forms, called 
indusium , which rises from the receptacle. 
The indusium is a plane, or vaulted, or cup-shaped membrane, 
produced from the receptacle of each sorus {special), and is gene- 
rally deciduous, or it becomes replicate. It is either produced 
from the centre of the receptacle (central), or on one side ( late- 
ral ), or its base is attached all round the base or margin of the 
receptacle (calyciform). When central it is usually orbicular, 
with its margin depressed, and free all round, or sometimes it is 
inflated. When lateral it is either reniform, oval , or oblong, and 
attached by a point or depressed sinus of its side ; or linear, and 
attached its whole length on the side of an elongated receptacle ; 
