44 ANNALS OF SCOTTISH NATURAL HISTORY 



Since writing the above, I have again gone over carefully 

 my collection of Dicrana from Carsaig, and have alighted 

 upon another whose characters cannot be reconciled to those 

 of D, conges tum or D. Fergusoni. 



In this, the areolation approaches closely that of 

 D. Scottianmn as well as of D. fnscescens, viz. cells near base 

 oblong, .03 to .04 by .007 to .01 I mm., rapidly lessening in 

 size upwards until, in the upper half, they are .006 to .009 by 

 .005 to .007 mm., and densely packed together. The nerve 

 is thick, and occupies about one-fourth the breadth of the leaf 

 near the base ; it tapers upwards and is lost a little below the 

 apex, instead of being excurrent as in the other. The 

 margins of the relatively shorter leaves are largely, and 

 more or less sharply, serrated in the uppermost fourth as 

 well as the corresponding back of the nerve nodulose. The 

 alar spaces are well developed, and are composed of large 

 brown cells with thick walls. In places the cylindrical pores 

 are numerous, lateral as well as apical ; and they are seen 

 farther up the leaf than usual, even connecting the smaller 

 cells. This moss may meanwhile be named Dicranum 

 subnitescens. 



Apart from the presence of pores, or rather tubes, this 

 Dicraninn, and probably the preceding one also, might 

 merely be reckoned forms of D. fnscescens, just as 

 D. congestum had previously been reckoned. The latter 

 is now classified in a different section from D. fuscescens, 

 viz. under that of which D. scopariuin may be said to be 

 the type. Whether the presence of these slender connect- 

 ing tubes in any Dicranum should continue to mark such a 

 sharp line of distinction is another question. Meanwhile I 

 am compelled to follow the general trend of opinion and to 

 act accordingly. I must confess, however, that I have not 

 yet detected these tubes in the leaves of specimens of true 

 D. fnscescens. In my opinion, the porous system of this 

 section of the Dicrana requires thorough revision, not only as 

 regards the existence of such tubes in other and different 

 species, but also as regards their physiological significance. 

 They are very slender, not more than .002 mm. in breadth, 

 and are easily ruptured, hence their detached groupings. 

 Their previous existence is supposed to be indicated by 



