322 GENERAL MORPHOLOGY OF PLANTS 



tective covering for the capsule while it is young. Finally the 

 egg case is torn away at its base and is raised aloft on the capsule 

 to form the hood or cap (the calyptra). With the ripening of the 

 spores in the capsule, the life history is complete, and the capsule 

 opens by the lid to permit their escape. In some of the lower 

 mosses there is no lid on the capsule, and it opens irregularly. 



489. The peat mosses. The peat mosses belong to a dis- 

 tinct order (Sphagnales) of the mosses. They are. called peat 

 mosses because the accumulation of the dead parts for centuries 

 forms one kind of peat. They grow in moors (or bogs) where 

 there is an abundance of water, or in very damp places in woods, 

 or even on the faces of rocks where water is constantly trickling 

 down. The protonema is thallose, and the leafy stem arises from 

 this as a branch. They continue to grow and branch year after 

 year, the stems dying away below. Because of the great quan- 

 tity of water in their tissues and in the ground, decay is slow 

 and only partial, because the water largely excludes the air 

 which is necessary for the activity of the bacteria and fungi which 

 cause the decay of vegetation. Their partially decayed remains 

 then form the peat. The quantity of water held by the peat 

 mosses can be seen by squeezing a handful, when an abundance 

 of water is wrung out. The peculiar character of the peat mosses 

 which enables them to hold water is as follows : There are numer- 

 ous lateral feathery-like branches which stand out straight from 

 the main stem. These are the primary branches. Secondary 

 branches arise from these close to the main stem and hang 

 downward around it. In the leaves there are dead cells alter- 

 nating with the green living ones. These dead cells have lost 

 their protoplasm, have numerous perforations in their walls and 

 also thickenings. As the plants stand close together in dense 

 tufts or swards, and the leaves are crowded together especially on 

 the pendent branches, capillarity draws water up from below 

 and it is stored in these empty dead cells.' With the partial 

 decay of the vegetation in these peat moors there is an abun- 

 dance of humic acid which also assists in preserving the material 

 from further decay. Peat is sometimes pressed into firm blocks 



