BRYUM. 315 



unites obviously unallied species while separating others as 

 clearly akin. 



The plan I have endeavoured to follow in the succeeding 

 arrangement is to separate off certain distinct groups clearly 

 defined either by a marked habit (such as Anomobryum and 

 Rhodobryum) or by an important character of the peristome (as 

 in Ptychostomum) ; and to divide the bulk of the species, then 

 remaining, into two groups into which they naturally fall, each 

 marked by a general concourse of characters rather than by any 

 one or more clearly defined differences of structure. For con- 

 venience of reference these Sections are tabulated below. 



One or two suggestions may be of use to the student in the 

 examination of these mosses. To examine the structure of the 

 outer peristome it is usually sufficient to flatten out an open 

 capsule in water under a cover-glass and to expel the air by 

 warming, but this is not satisfactory when it is required to ob- 

 serve the colour of the base of the teeth, nor for the examination 

 of the inner peristome ; it is best therefore to separate the whole 

 peristome as near as possible to the mouth of the capsule, when it 

 may be separated easily into two halves and spread out flat on 

 the slide. In examining the capsule to determine whether or not 

 it is contracted below the mouth it is absolutely necessary to ob- 

 serve perfectly ripened capsules, and if possible such as have lost 

 their lids before gathering ; in immature capsules, even where 

 apparently ripe, a contraction invariably takes place below the 

 more firmly textured mouth upon drying, and this will almost 

 always be found to be the case with specimens gathered before 

 the fall of the lid, while capsules on the same tuft which had 

 ripened fully and lost their lids before gathering will show no 

 trace of this contraction. Indeed it is probably not too much to 

 say that the species in which this contraction is normal in fully 

 ripened capsules, as in B. turbinatum, are extremely few and 

 even exceptional. It may be added that very little reliance is to 

 be placed on the obtuseness or acuteness of the lid in this genus, 

 as it often exhibits considerable variation in this respect even 

 within the limits of a single tuft. 



A. ANOMOBRYUM. Innovations slender, julaceous ; leaves 

 small, sub-equal, concave, closely imbricated; upper cells very 

 narrow, linear. 



B. PTYCHOSTOMUM. Innovations not julaceous ; cells 

 wider, more or less rhomboid-hexagonal. Inner peristome im- 

 perfect, the cilia being absent or very rudimentary and without 



