POLYTRICHUM THE SPOROGONIUM 187 



2. Above this is the real capsule in which will be recognized 

 as before in the transverse section : 



a. The wall of the capsule. 



b. The outer air-space traversed by filaments. 



c. The spore-sac with structure as before described. 



d. The inner air-space. 



<?. The central columella. 



These severally terminate below in the tissue of the apophysis : 

 above they may be traced to a point close below 



3. The opercuium, which appears as a conical lid, at the apex 

 of the capsule. 



4. Note carefully a transverse band of tissue of pale, com- 

 pressed cells at the base of the columella : this is the epiphragm 

 mentioned on p. 180, which remains after the opercuium is 

 removed. At the margin of it, will be seen 



5. The peristome, consisting of a series of curved cells with 

 their walls more or less thickened according to age. 



In order to see the condition of the epiphragm in the mature 

 capsule, and its connection with the teeth of the peristome, take 

 a ripe specimen from which the opercuium has dropped off. 

 With a sharp razor cut transversely through the capsule so as to 

 remove the epiphragm : mount in water and examine under a 

 low power. Note that the epiphragm is a thin papery tissue, 

 without intercellular spaces. The peristome consists of 64 teeth, 

 connected below with the wall of the capsule, above with the 

 margin of the epiphragm. By drying up of thinner walled cells 

 between the teeth, spaces are formed through which the spores 

 can escape. The capsule becomes inverted at the period of 

 ripeness, and the dry spores are dusted out through these 

 spaces. 



In many respects Polytrichum is more complex than other. 

 Mosses, and differs from most in the characters of the peristome. 

 Other examples of Mosses are described in the larger edition pp. 



342355- 



XV. Scatter spores from the ripe sporogonium of Polytri- 

 chum or of some other Moss over moist soil, and keep them at 

 a moderately high temperature, under a bell-glass, for a few 

 days. The surface of the soil will soon be seen to be over- 



