BRITISH MOSSES. 



43 



theless, I hope, prove of some assistance to those beginning 

 the study. 



The object served by the complicated structure of the 

 peristome is not, perhaps, very certain, but it seems to be 

 intended to secure the retention or exclusion of the spores 

 from the spore sac in such conditions of the atmosphere 

 as will best conduce to their germination. In the 

 Gymnostomous Mosses (i.e., those without peristome) it is 

 observed that the spores sometimes germinate within the 

 capsule, an event which is probably adverse to the 

 prospects of the race. The following table will illustrate, 

 in a few cases selected as illustrations, the different 

 behaviour of the teeth of the peristome under different 

 hygrometric conditions, and suggests what is the probable 

 advantage in each case : 



TABLE D. 



The motion of the teeth of the peristome appears to be 

 due to the action of the annulus, a ring of specialized 



