6 INTRODUCTION. 
In order to avoid any obscurity in the use of the various terms, 
there is here added the following short description of the struc- 
ture of the various portions of a Moss which are available for the 
purpose of arranging the species in genera and natural groups. 
A Moss is composed of the following parts :— The stem, which 
is either short or elongated, erect, rooting only at the base, fer- 
tile from the apex, and continued by innovations arising below 
the inflorescence, or it is procumbent, creeping, rooting through- 
out its length or at intervals, and fertile on abbreviated proper 
branches; or it may have a creeping primary stem and erect or 
ascending branches, fertile at their apices, or from their sides. 
When the stem is very short, it is usually fleshy and but little 
indurated, but when much elongated it is frequently hard and 
woody. The leaves are inserted across the stem at a right angle 
with its axis, or sometimes obliquely, more rarely parallel with it. 
They are composed of a single layer of cells all uniform in struc- 
tuve (Homodictye), or of two kinds of cells diverse in form as 
well as in their contents ( Zeterodictye), and have one or two 
nerves or are entirely nerveless ; in some instances the nerve is 
so much enlarged that it constitutes in itself almost the entire 
leaf. In Mosses with erect stems and terminal fructification the 
leaves are frequently increased in size towards the inflorescence ; 
but those immediately surrounding the organs of reproduction 
are usually of'a different form, and composed of differently formed 
cells, from those of other portions of the stem. 
The male inflorescence consists of antheridia—small cylindrical 
oblong bodies opening at their apices for the emission of their 
contents (the spermatozoids), very minute bodies consisting of 
a spiral fibre with an exceedingly minute globular body attached 
to its middle ; and these at maturity are possessed of spontaneous 
motion. These antheridia are intermixed with hyaline articu- 
lated filaments or paraphyses, and, with them, are enclosed by the 
perigonal leaves in a small bud-like flower (flos gemmaceus), or are 
surrounded at the apices of the stems by short spreading leaves 
leaving the antheridia visible from above (flos discoideus). The 
female inflorescence consists of archegonia—small flask-shaped 
bodies of the same colour as the antheridia, and like them mixed 
with paraphyses. In some species both male and female organs 
are found in the same flower (flores synoici). After fertilization 
the archegonium increases in size and length, its contents, at 
first imperceptible, gradually increase, and at length the en- 
