28 ANDRE/EACE/E. 



In reading the descriptions given by various authors of this plant, one cannot but 

 be struck with the uncertainty of the characters relied upon to distinguish it ; what is 

 held by one writer to be a distinctive character being held of no importance by 

 another, so that one is compelled to doubt its stability as a species ; and an examina- 

 tion of a considerable number of specimens has entirely confirmed me in this view ; 

 indeed, after carefully examining a large number of leaves of A. Rothii and of the 

 present plant I am inclined to doubt whether it has a full title even to the rank of a 

 sub-species of the former. According to Braithwaite, the leaves are of almost exactly 

 the same form as in A. Rothii, or its var. hamata, only very narrow and subulate in 

 the upper part, and with the nerve apparently excurrent as a papillose subula ; but 

 even this seemingly important distinction disappears when on closer examination it is 

 found that the lamina is really continued to apex in a single series of cells. Now, I 

 have frequently found forms of A. Rothii, and especially its var. falcata, to have the 

 limb of the leaf more than usually narrow, with only two series of cells in its upper 

 part ; indeed, according to C. Mtiller, the var. falcata has the nerve " occupying the 

 whole apex." The form of the leaf-base, oblong and gradually narrowed above, can- 

 not be held characteristic, since in what are, I suppose, fairly typical specimens of A. 

 crassinervia, viz., those gathered by Arnell at Hernosand, Sweden (Musci Gallia, 

 No. 697) ; the leaf-base is oval and quickly narrowed above, almost as in the var. 

 falcata. The more regular, quadrate cells with thinner walls, held of importance by 

 Boulay, may also be found in forms of A. Rothii. Again, with regard to the excur- 

 rence of the nerve, I have hardly ever found a leaf with the lamina really ceasing 

 below the apex, except in old leaves where it had possibly been removed by erosion ; 

 in the large majority of cases where it appears excurrent I have found on close ex- 

 amination distinct indications that the single row of marginal cells has been so eroded ; 

 and the papillosity of the subula in every case in which I have observed it, has been 

 due to the slight erosion of the cell walls of this row of cells, as may often be found in 

 the older leaves for a considerable distance below the apex ; I have never seen a 

 young or unworn leaf with any trace of this papillosity. The width of the nerve I 

 have also found variable. 



The differences must therefore, I think, be held to be of a very slight nature, and 

 A. crassinervia must be considered to be little more than a variety of A. Rothii with 

 an extremely narrow lamina reduced to one or two series of cells above and occa- 

 sionally disappearing entirely just below the apex. Boulay (Muscinees de la France) 

 describes the true A. crassinervia as having the nerve excurrent from below the 

 middle of the leaf, a character sufficiently defined to separate it as a sub-species at 

 least, although the other points which he holds characteristic are certainly of slight 

 importance ; but this form, or anything approaching it, has, I believe, never been 

 found in Britain, and we must either exclude A. crassinervia from our list altogether 

 or consider it, with Braithwaite and other authors, as including forms with a very 

 narrow lamina continuous to apex, this feature and the general narrowness of the limb 

 distinguishing it from A. Rothii, which, however, certainly passes into these less 

 marked forms. 



In support of this view we have the fact that Wilson always maintained that the 

 three forms only constituted a single species ; also that the plant described as A. 

 Huntii by Limpricht has been variously placed as a variety by some authors under 

 A. falcata, by others under A. crassinervia. No doubt much confusion has arisen 

 from the distribution of wrongly-named specimens ; this was the case with No. 394 of 

 the Musci Gallia, which is only a form of A. Rothii with the lamina quite distinct to 

 the apex ; and I have found the same feature in specimens supposed to be typical 

 crassinervia, gathered by Whitehead on Penyghent. 



The var. Huntii is described by Macoun as differing from A. crassinervia " prin- 

 cipally in the subula of the leaf, only about a half formed by the costa, and the very 

 papillose perigonial and perichaetial leaves ; " and he adds that it is often confounded 

 with A. Rothii. Schimper, too, referred it to A. falcata. 



B. Chasmocalyx. 

 Perichaetial bracts like the leaves, distinctly nerved. 



