MOSSES 



349 



by a hairy, conical cap or hood (the calyptra). When the hood 

 is removed the appearance of numbers of these capsules on their 

 slender stalks perhaps suggested the name of " pigeon wheat." 



Fig. 310. Fig. 311. 



Section through end of stem of female plant Antheridium of 

 of Mnium, showing archegonia at the center. Mnium with jointed 

 One archegonium shows the egg. On the paraphysis at the 

 sides are sections of the protecting leaves. left; sperms at the 



right. 



At the apex of the capsule is a minute " lid " (the operculum) 

 which is easily removed, exposing the " mouth " of the capsule 

 (the stomium). Around the edges of the mouth are numerous 

 minute pointed processes, the teeth, 64 in one circle or row. 

 There is another inner row of thinner teeth. 



502. Many mosses have a double row of teeth, others have 

 but a single row, while some have no teeth. In one little moss 

 common on decaying logs in woods there are only four teeth 

 (Tetraphis pellucida = Georgia). Some have 16, others 32, etc. 

 The teeth are usually very sensitive to changes in the humidity 

 of the air, spreading apart in moist weather, thus permitting the 

 spores to escape, or closing in dry weather. The spores are 

 formed in a special spore-bearing tissue, which is in the form of a 

 hollow tube in the middle part of the capsule. The tube is filled 



