18 HISTORY OF BRITISH MOSSES. 



substance, such as the edges and surface of their leaves. 

 There is no instance in which straight or tap roots are 

 produced, though the primary and secondary can be dis- 

 tinguished in some cases. The roots of Mosses, as we 

 have already seen, are the chief origin of the soil formed in 

 peat-bogs and other localities in which they abound, and thus 

 they perform an important part in the economy of nature. 



In no particular do Mosses present us with a greater 

 variety, than in the length, direction, and form of their stems 

 and branches, for wliile some grow to the extent of several 

 feet, others seem to be entirely destitute of any trace of a 

 stem, leaving the fruit-stalk rising almost directly from the 

 disc or root. Again, if we look at the direction they take, 

 we find the Hypmims, with various allied genera, branching 

 out more or less irregularly on banks, trees, or rivulets. 

 Others, as the genus Orthotrichum, send out numerous 

 branches from a common centre, some of its stems being 

 erect, while others spread around at various angles, and 

 make a nice semicircular cusliion or tuft; while a third 

 class, comprising a great many genera with very short 

 stems, grow in extensive patches on the ground and wall- 

 tops, each individual made up of its simple rootlets, stem, 

 and fruit-stalk. 



