CHAP. III. 
MOSSES. 
267 
tigated, it will be found that the centre is occupied by an 
axis, called the columella; and that the space between the 
columella and the sides of the sporangium is filled with 
sporules. The brim of the sporangium is furnished with an 
elastic external ring, or annulus, and an interior apparatus, 
called the peristomium : this is formed of two distinct mem- 
branes, one of which originates in the outer coating of the 
sporangium, the other in the inner coat; hence they are 
named the outer and inner peristomia. The nature of the 
peristomium is practically determined at the period of the 
maturity of the sporangium. At this time both membranes 
are occasionally obliterated ; but this is an unfrequent occur- 
rence : sometimes one membrane only remains, either divided 
into divisions, called teeth, which are always some multiple 
of four, varying from that number as high as eighty, or 
stretching across the orifice of the theca, which is closed up 
by it ; this is sometimes named the epiphragma or tympanum. 
Most frequently both membranes are present, divided into 
teeth, from differences in the number or cohesion of which 
the generic characters of mosses are in a great measure 
formed. For further information upon the peristomium, see 
Brown’s remarks upon Lyellia, in the 12th volume of the 
Linnean Transactions. 
M. Endlicher considers that the sporangium is formed by 
the adhesion of an external and internal series of organs; 
and he calls sporangidium the inner, to which the peristomium 
belongs. [Genera Plantarum, 46.) 
The interior of the sporangium is commonly unilocular; 
but in some species, especially of Polytrichum, it is separated 
into several cells by dissepiments originating with the colu- 
mella. 
If at the base of the sporangium there is a dilatation or 
swelling on one side, this is called a struma ; if it is regularly 
lengthened downwards, as in most of the Splachnums, such 
an elongation is called an apophysis. 
In Andraeaceae the sporangium is not an urn-like case, but 
splits into four valves, cohering by the operculum and base. 
The spores have no adhesion either to the sides of the 
sporangium or to the columella, but appear to be formed 
