884 DR R. KIDSTON AND PROF. W. H. LANG ON OLD RED SANDSTONE PLANTS 
as result from cell-division and in being largely composed of relatively wide tubular 
elements, between which, and most characteristically in the medullary spots, there is 
a system of delicate, narrow, interlacing tubes. 
The Rhynie species differs * from N. Logani in the absence of radial bands and 
the presence of “ medullary spots.” In N. Storriei, although there are “ medullary 
spots,” the large tubes are always separated by a slight space, are smaller, and have 
thinner walls. With N. Ortoni it agrees in the presence of “ medullary spots,” but 
the wide tubes of that species are larger, attaining a maximum diameter of 67 m, 
and are more uniform in size. The thick walls of the Rhyme species show some 
similarity to those of AT. crassum, but the wide tubes are larger in the Scottish 
species and the cavity is always prominent. 
From N. laxum and N. tenue , as described by Penhallow, it appears to be dis- 
tinguished by several characters. The preservation of these forms and of N. Hiclcsii 
and N. Dechenianum is, however, too imperfect to admit of detailed comparisons. 
Such specific distinctness, interesting as it is, is secondary in importance to the 
recognition in this deposit of an example showing the characteristic construction of 
this type of plant. The diagnosis will be given after the description of the second 
fragment. 
Of the second fragment there were also two sections, one of which shows the 
tissues rather better preserved than the other, though both are instructive. The 
greater part of the better section is represented, magnified 30 diameters, in fig. 113. 
As this shows, the fragment includes a portion of the outer surface of the plant 
and the tissue lying beneath this. The curvature of the surface indicates that the 
part of the plant was cylindrical (or less probably spherical). If we assume it to 
have been cylindrical, the curvature indicates a diameter of about 1 ’2 cm. 
The following structural regions can be distinguished proceeding from the outer 
surface inwards : (a) a narrow, clear, structureless zone ; ( b ) a zone about 1 mm. in 
depth, composed of tubular filaments standing at right angles to the surface ; (c) 
an inner region in which the tubes or filaments run irregularly ; these tubes are 
continuous with those of zone b. A number of small areas of different texture, that 
appear as dark spots in the figure, are distributed through this region. The same 
zones are shown rather more clearly in fig. 114. 
The chief structural component of the inner tissue (zone c ) has the form of 
branched tubes or filaments running irregularly in all directions and crossing one 
another so as to give the effect of a reticulate structure (figs. 115 and 116). These 
filaments when best preserved stand out by reason of their brown colour and homo- 
geneous appearance. This seems referable to a preservation of the contents rather 
* It will be sufficient to give a general reference to the diagnoses of N. Logani, N. Hicksii, N. crassum, N. laxum, 
and N. tenue in Penhallow’s paper {Trans. Canad. Roy. Soc., vol. vii, 1889, p. 28) ; to that of N. Ortoni, in a paper 
by the same investigator (Ann. Bot., vol. x, 1896, p. 41) ; and to that of N. Dechenianum, in the paper by Solms 
(Jahrb. d. k. preuss. Geol. Landesanstalt, 1894). 
