RHACOMITRIUM. 153 



habit of that plant is quite different. So much doubt exists as to the plant intended 

 by Bridel to be described by his name R. microcarpon, that it seems safer, and is far 

 less confusing, to use Lindberg's name for the present species and R. sudeticum for 

 the second of the two plants to which Bridel's name has equally been applied. 



6. Rhacomitrium heterostichum Brid. (Trichostomum 



heterostichum Hedw. ; Grimmia heterosticha CM., Braithw. 



Br. M. Fl.) (Tab. XXIV. A.). 



Typically a rather short-stemmed plant, growing in close 

 tufts, erect or more usually depressed, at the outside of the 

 patches prostrate, rigid, greyish green, hoary ; stems dichotomously 

 branched with few branchlets which are usually slender and spread- 

 ing rather than short and nodose ; leaves spreading or subsecund, 

 erect but not appressed when dry, rather short and broad, oblong- 

 lanceolate from a wide base, gradually narrowed to a rather broad 

 point, the summit of which usually has a hyaline tip with decurrent 

 edges and is prolonged into a broad flat hair, which is denticulate 

 at the margins, and often longer than half the rest of the leaf ; 

 leaf-margins revolute to apex, slightly incrassate above ; nerve 

 distinct, reaching apex and passing into the hyaline point ; lower 

 cells linear, nodulose, a few at basal margin pellucid, upper 

 gradually shorter, broader than in the last two species, near apex 

 shortly rectangular , rounded, or sub-quadrate , usually 1^—3 times 

 as long as broad, shorter at margin, incrassate and sinuose below 

 the surface, not papillose. Calyptra papillose at apex ; seta 

 straight, reddish, capsule oblong-cylindric, narrowed at the 

 mouth, thick-walled, brown. Peristome teeth rather short, 

 lanceolate, unequally divided. 



Var. jB. alopecurum Hiibn. (Grimmia affinis Lindb., Braithw. 

 Br. M. Fl.). Slender and elongated, with more numerous slender 

 fasciculate branches ; less hoary, of a darker colour. Leaves 

 more acute, the hair-point shorter, £ length of leaf, often almost 

 obsolete. Capsule shorter, peristome small. 



Var. y. gracilescens B. & S. (G. affinis var. gracilescens 

 Lindb., Braithw. Br. M. FL). Still more slender, with longer, 

 often fastigiate branches, sometimes almost simple or only slightly 

 dichotomous ; hair-points very short, often wanting ; capsule 

 smaller than in the last variety, often paler and thinner-walled. 



Hab. Rocks and walls in mountainous districts. Common. Fr. summer. 



Rhacomitrium heterostichum is our most variable species, and the multiple forms 

 are so inconstant and so ill-defined as almost to defy classification. They depend 

 chiefly on the mode of ramification, the relative length, or absence, of the hair-point, the 



