INTRODUCTION. 



Mosses are found in various situations, and may be described 

 as terrestrial, rupestral, arboreal, aquatic, paludal, etc., according 

 to the matrix or the locality which they prefer. These terms, 

 however, must not be taken too strictly, for while almost every 

 species manifests a decided preference for one kind of matrix or 

 environment, and whole classes of allied mosses are often linked 

 together by a common preference of the kind, yet it rarely 

 happens that a given species, whatever its natural habitat, may 

 not occasionally be found in some other, more unusual situation. 

 As a general rule, however, the habitat of a moss may be looked 

 upon as an important aid in determining its identity, and in all 

 doubtful cases the soil or other matrix should be entered upon the 

 label, with the locality. 



The habit of the moss and its manner of growth, whether the 

 separate plants are scattered singly, clustered or gregarious, or 

 more or less densely tufted, are also points of importance and 

 should be noted at the time of collecting. 



The Vegetative Organs. 



Mosses always consist of a stem and leaves, though either of 

 these structures may be so reduced in size as to be inconspicuous. 

 A certain ambiguity in the use of the terms " stem," "branch," 

 should be here pointed out. They are frequently used, and are 

 employed in this work, in a double sense, either as designating 

 the actual solid cylinder upon which the leaves are arranged, or 

 as embracing the whole visible structure, leaves included. Thus 

 in speaking of the cuticular cells of the stem of Sphagnum, the 

 first and more restricted meaning of the word is understood ; 

 whereas when a stem is spoken of as tumid or inflated, it is the 

 whole structure, stem and leaves together, that is referred to. 

 The absence of any convenient term to express the latter con- 

 ception renders this extension of the words somewhat desirable, 

 and they will, I believe, in no case give rise to confusion. 



The different modes of branching in different mosses are 

 perhaps among the first things to strike the beginner, owing to 

 the very different results they produce in the general appearance 

 of the mosses. There are two main types of branching by which 

 all mosses may roughly be divided into two classes. In the one 

 the stem is typically erect, simple, slightly forked, or with more 

 numerous lateral branches, but producing the flowers and later 

 the fruit at the apices of the stem and of at least the principal 



