7 
Conducting Tissue-System in Bryophyta. 
has a creeping rhizome-like isodiametric basal part, and from 
it arise the flat assimilating fronds, each of which is often 
spread out by repeated shortened dichotomy into the shape 
of a fan. Farmer (op. cit.) has pointed out the probability of 
the parallel development of this habit in the different genera. 
Of the less differentiated species of P allavicinia, Schiffner 
separates two, P. Blyttii and P. hibernica , from the others, 
by reason of their having no axial strand in the midrib (sub- 
genus Morckia , Gottsche gen.). Of these the latter, as 
originally described by Hooker (op. cit., Plate LXXVIII), is 
mainly separable from P. Lyellii , the other British species, by 
this character, but there seem to be several distinct forms con- 
fused under the name Hibernica. In specimens from Hooker’s 
type from Loughbray, Co. Wicklow, and in specimens from 
Yorkshire, of quite different habit, which Mr. W. H. Pearson 
tells us agree with Gottsche’s Morckia hibernica we have 
found the tissue of the midrib quite homogeneous without any 
trace of an axial strand. In another plant, however, kindly 
sent us by Mr. David McArdle of the Royal Glasnevin 
Botanic Gardens, from sandy flats at Malahide, Co. Dublin, 
under the same name, but which he places under var. / 3 , 
Wilsoniana , Carrington, we find two distinct lateral strands 
in the midrib, each consisting, in transverse section, of about 
twenty cells which do not differ from the surrounding tissue 
in width or in the thickness of their walls. These walls, 
however, are distinctly brown in the unstained condition, and 
hold aniline stains more strongly than the surrounding 
tissue (PI. I, Fig. i). On longitudinal section many of the 
strand-cells do not differ greatly in shape from the neigh- 
bouring cells, but they tend to be longer, and some are of 
considerably greater length (Fig. 2). Occasionally a very 
thin colourless cross-wall may be seen, as at a in Fig. 2. In 
none of these cells have we found nuclei, though they often 
possess a little contents, apparently scanty remains of proto- 
plasm, as far as can be made out from herbarium-material. 
In the absence of living material on which to experiment, 
we regard these strands as very primitive water-conducting 
