TRUE MOSSES (BRYALES) 417 



growing out so as to form leaves, then a leafy sporophyte like 

 those of Pteridophytes would be formed. In the third place 

 there is a meristematic group of cells at the base of the sporophyte 

 by which growth and production of spores are maintained for a 

 period of time. 



Mosses 



General Description. — In general, Mosses do not need so much 

 moisture as Liverworts do, and are, therefore, more generally 

 distributed. They are common in moist places and some inhabit 

 bogs and streams, but Mosses are also very common in dry 

 places. They live on tree trunks, logs, stumps, rocks, soil, and in 

 bogs and fresh water. In fact one can find Mosses nearly every- 



* where. They often mass together in clumps and cushion-like 

 masses which hold water much like a sponge. Many Mosses, 

 especially those growing in dry places, can become dried out and 

 then revive when they become moist again. The Mosses as a 

 group have better differentiated gametophytes and sporophytes 

 than the Liverworts. 



The Mosses are divided into three groups, Sphagnales, Andrea- 

 les, and Bryales. The Sphagnales are the Sphagnums, which live 

 in bogs where the accumulation of their plant bodies forms peat. 

 The Andreales are a very small group of siliceous rock Mosses 

 which will receive no further discussion, although they are inter- 

 esting because they present a combination of characters which 

 relate them to the Sphagnales, Bryales, and also to Liverworts. 

 The group containing the vast assemblage of our most familiar 

 Mosses is the Bryales. The Bryales, known also as the True 

 Mosses, are the most highly organized of the Mosses. 



True Mosses (Bryales). — The most conspicuous part of the 

 Moss plant is the gametophyte, which looks like Figure "372. It 

 consists of a leafy stem attached to the substratum by rhizoids. 

 In some Mosses the leafy stem is prostrate, but in many it grows 

 erect. The leaves of the Moss plant, like the leaves of the foliose 

 Liverworts, are quite simple. In most part they are only one 

 cell in thickness. They have no stomata and no palisade or 



. spongy tissues. Although they are called leaves, it is obvious 

 that they are not like the leaves of the higher plants. But their 

 cells contain chloroplasts and they make carbohydrates just as 

 the leaves of the higher plants do. Stomata, paUsade, and 



