X INTRODUCTION. 



colours. They may be produced, sporadically, upon the leaves or 

 other parts of the plant, and they hardly differ morphologically 

 from the chlorophyllose threads of the protonema ; this is the 

 branched network of conferva-like filaments produced by the 

 germination of the spores, and from which is developed the moss 

 plant ; the protonema usually disappears at an early stage in the 

 life of the moss, but in some of the smaller species it is persistent 

 for a considerable period (Tab. \ . 3). 



In addition to the radicular fibres and the leaves, the stem is 

 occasionally clothed with appendages of another kind, intermixed 

 with the leaves; these are called paraphyllia, and are green, 

 multiform, leaf-like or thread-like structures, sometimes formed 

 like miniature leaves, at others deeply cut, fringed, or so slender 

 as to resemble branched threads (Tab. I. n, 13). 



The leaves of mosses are of various forms, and the shape of 

 the leaf affords, all things considered, one of the most important 

 specific characters of mosses ; a reference to the glossary and to 

 the figures will illustrate the various forms and explain the terms 

 used, which need not be recapitulated here ; but it may be 

 remarked that the leaves are always sessile, never stalked, and in 

 outline range from subulate to orbicular, with almost every 

 intermediate form ; that they are never compound, nor even 

 lobed, though frequently serrate in various degrees, or sometimes 

 laciniate. There is no epidermis or cuticular tissue, and the 

 whole leaf is almost always formed of a single layer of cells 

 {v. section, Tab. III. 19, 20), rarely in part or altogether of a 

 double layer (Tab. III. 24), with the exceptions of the nerve (or 

 mid-rib) which when present is composed of narrow and elongated 

 cells often of several layers in thickness and frequently showing 

 some differentiation in structure, and of the marginal border 

 which in certain groups of mosses is formed of different cells from 

 those which cempose the rest of the leaf, usually, in such cases, 

 being more like those of the nerve (Tab. III. 10, 21). 



The leaves may be more or less decurrent at the base, the 

 lamina running down t*he stem for some distance on each side 

 below the insertion or line of juncture of the leaf-base with the 

 stem ; this is sometimes so conspicuous that the stem is distinctly 

 winged (Tab. II. 7) ; in certain groups it is a character of great 

 importance, and in such cases the leaf should be separated with 

 great care from the stem, in order that the decurrent part, or a 

 portion at least, may be detached also. As a rule however the 

 degree of decurrence can best be observed by stripping the 



