CHAPTER XII 



THE BRYOPHYTA; MUSCI, THE MOSSES 



The Musci are Bryophyta in which the body is characteristically divided into 

 stem and leaves. The former may be erect or prostrate, and the leaves may 

 be very small and little more than short green outgrowths, or they may be 

 fiat and expanded, like miniatures of the leaves of higher plants. In the 

 anatomy of the stem there is a certain amount of tissue differentiation, but 

 no true vascular system is developed. Cellulose is rare in the cell walls, 

 which are composed chiefly of hemicelluloses and pentosanes. The sex 

 organs are either produced on separate plants or on separate branches, or 

 even on the same branch of the same individual, immersed in a group of leaves 

 at the apex of the branch, and this structure is sometimes referred to as the 

 " flower." As a result of fertilization a sporophyte is developed which 

 consists of a stalk and a capsule in w^hich the spores are enclosed. This 

 capsule is often highly specialized. It possesses stomata and chloroplasts, 

 which distinguish it from the corresponding structure in most of the 

 Hepaticae. 



The spores on germination give rise to a filamentous structure, termed a 

 protonema, somewhat resembling in appearance the thallus of Vaucheria, 

 and from it the numerous leafy shoots arise which compose the mature 

 Moss plant. 



The fossil history of the Mosses goes back as far as the Carboniferous 

 times. In the Mesozoic there are only very scanty remains, but in the lower 

 Tertiary a number of peculiar forms have been found embedded in amber 

 of Eocene age. In the Pliocene there are remains of forms still living at the 

 present day. 



The Musci are divided into three orders of which we shall consider 

 examples of two : — 



1. Bryales {e.g., Mnium,Polytrichuni). 



2. Sphagnales {e.g., Sphagnum). 



Bryales 



The Bryales is by far the largest order of the Mosses and includes nearly 

 all the common families. They are characterized by the fact that both the 

 columella and the spores are developed from the inner tissues of the 

 sporogonium. The spore sac is separated from the wall of the capsule by 

 an air space. The capsule dehisces either by a lid or irregularly. 



We shall consider two examples of this group, Mnium horrmm and 

 Polytrichum commune. 



415 



