SHOWING STRUCTURE, FROM THE RHYNIE CHERT BED, ABERDEENSHIRE. 605 
peat, composed of partly decayed stems of R. major , with sporangia of that species, 
and were evidently preserved as they grew at one level of the peaty mass. The 
presumption is that they belong to R. major and not to R. Gwynne-Vaughani, no 
stems of which are found in this block. This conclusion, though confirmed by some 
details, would be difficult without the evidence afforded by association. Rhizomes 
of R. major have, however, now been met with in other blocks, and rhizomes of 
similar type, though smaller, which undoubtedly belong to R . Gwynne-Vaughani 
will be described below. 
Additional Notes on Rhynia Gwynne-Vaughani, Kidston and Lang. 
(PL I.) 
1917. Rhynia Gwynne-Vaughani, Kidston and Lang (pars), Trans. Roy. Soc. Edin., vol. li, p. 7 G ♦ , 
pi. ii, figs. 2-5 ; pi. iii, figs. 6-10; pi. v, figs. 20, 23-30; pi. vi, figs. 31-36, 38-40; pi. vii, 
tigs. 41-51 ; pi. viii, figs. 52-61 ; pi. ix, figs. 63-63a; pi. x, figs. 72-74. 
Many of the features of R. Gwynne-Vaughani were sufficiently described and 
illustrated in Part I, and only some supplementary notes are required. 
Since there is reason to regard all the rhizomes described in Part I as of R. major, 
a rhizome belonging to R. Gwynne-Vaughani is figured here (PI. I, fig, l). The 
rhizome, which is cut transversely, has given off laterally an ascending stem. This 
rhizome has a thin-walled epidermis, a slight but evident distinction between outer 
and inner cortex, and a small stele, the xylem of which consists of about four 
tracheides. Rhizoids extend downwards into the peat from the epidermis of the 
lower side of the rhizome. The ascending branch shows epidermis, cortex, phloem, 
and xylem ; it agrees in size and structure with the typical stems of R. Gwynne- 
Vaughani making up the peat of this region of the bed. Comparison with the 
rhizomes of R. major in Part I will show the essential similarity in structure of this 
region of the plant in the two species, and the difference in size. 
We have little to add to the description of the stem in Part I, which was based 
almost entirely on this species. It may, however, be pointed out that, while the 
small strand of xylem is often uniform and composed of similar tracheides, this is 
not always the case. In larger- strands a distinction of smaller central tracheides 
surrounded by outer tracheides of greater diameter is evident. This distinction can 
be seen in figs. 41 and 45 on PI. VII of Part I. Attention is directed to this char- 
acter in R. Gwynne-Vaughani, since it will be found to hold regularly and strikingly 
for the steles of R. major and Hornea Lignieri. 
In the peat, composed of numerous stems of R. Gwynne-Vaughani, a number of 
cases have been noticed in which stems have been cut in the neighbourhood of their 
tips. The most striking example is shown in PI. I, figs. 2-4, and demonstrates the 
appearance of the growing point. Fig. 2 shows at a, among a group of typical stems 
of this species, one with its tip cut longitudinally. This tip is more highly magnified 
