INTRODUCTION. IX 



branches ; by this the apical growth of the stem is terminated, 

 and further development can only take place by new branches, 

 usually termed innovations, which are most frequently produced, 

 singly, in pairs or in whorls, immediately below the flower. The 

 tendency is therefore to grow upwards, and gradually to increase 

 the number of branches from an originally simple stem, and this 

 naturally conduces to the greater density of the tufts or cushions. 

 Mosses of this type are termed Acrocarpous (Tab. I. 5, 14 ; Tab. 

 II. 6). 



In the second type the stem whether little, or, as is usually the 

 case, much branched produces its flowers on the side, not at its 

 apex nor at that of the branches ; consequently the apical growth 

 of the stem is not terminated by the production of the fruit, but 

 becomes indefinite, and the stems frequently attain a very con- 

 siderable length. The natural consequence of this is that the 

 stems are rarely erect, but usually more or less prostrate or at 

 least arched. This gives a wider, less dense and less elevated 

 character to the tufts, which are often straggling. This is the 

 type of the Pleurocarpous mosses. (Tab. I. 4, 9, 10, 12). 



The beginner will very speedily recognise these two types in 

 the field ; they are indeed so distinct that it has usually been the 

 practice to make the distinction between Acrocarpous and Pleuro- 

 carpous mosses the primary division of the whole class ; this 

 cannot now be maintained, but the distinction between the two 

 types is of considerable practical assistance in the identification of 

 mosses, if of less theoretical importance than has sometimes been 

 held. 



In the Pleurocarpous mosses the branching is frequently 

 regularly pinnate ; sometimes the branches in these cases are 

 again branched, when the stem is bipinnate, and in a few cases 

 the process is again repeated, resulting in a tripinnate arrange- 

 ment ; this is never the case with the Acrocarpous mosses, where 

 the branching is either irregular, or more or less alternate, or 

 imperfectly dichotomous, sometimes, but rarely, distinctly whorled. 

 The innovations formed below the fertile flower frequently 

 develope so rapidly as to equal or overtop the capsules, which 

 then appear, but falsely, to be laterally produced. 



Mosses are not attached to their substratum by true roots, 

 but there are usually present rootlets or radicles which perform 

 the functions of roots, and are often produced throughout the 

 whole length of the stem, or over the greater part, frequently in 

 very great numbers so as to form a felt-like covering or tomentum ; 

 they are usually of a reddish brown hue, but may assume other 



