888 DR R. KIDSTON AND PROF. W. H. LANG ON OLD RED SANDSTONE PLANTS 
system can be traced into the medullary spots. These “ spots ” were about 
'2 to "3 mm. in diameter, and were originally occupied by narrow tubes about 10 m 
in diameter. 
Another fragment is regarded as the peripheral region of the plant. Internally 
it show T s interlacing tubes and small medullary spots (T5 mm.). The tubes bend 
outwards, and in the superficial layer, which has a thickness of about 1 mm., stand 
parallel and at right angles to the surface. Externally there is a narrow amorphous 
layer above the free terminations of the tubes. 
Locality . — Muir of Rhynie, Aberdeenshire. 
Horizon . — Old Red Sandstone. (Not younger than the Middle Division of the 
Old Red Sandstone of Scotland.) 
5. The Succession of the Plants as shown in one Complete Vertical 
Section of the Bed. 
The plant-containing chert was discovered by Dr Mackie, as has been men- 
tioned in previous papers, in the form of isolated blocks. The bed from which these 
came has since been successfully exposed by the Ceological Survey. An account 
of the excavations made for this purpose is given in a Report * of a Committee 
of the British Association. A set of blocks forming a complete vertical section 
from Trench No. 1 has been available for our investigation, and a general account 
of this section was included in Part I of this series of papers. Since then thin 
sections for microscopical examination of all the plant-containing beds of this 
vertical section have been studied. We are thus able to extend and qualify our 
earlier account, and to indicate more precisely the distribution of the plants 
throughout the chert-band at this one spot, where it was about eight feet in 
thickness. 
In the following description the numbering and lettering of the beds t as given 
in the section represented on pp. 762-3 of Part I will be adhered to, and the 
composition of the beds followed from below upwards. While the description 
will be based on the actual section in one vertical plane, variations in the 
succession of the plants, especially in the critical lower region of the bed, must 
be taken into consideration. The information afforded by certain loose blocks 
referable to this region can suitably be included in the description. 
Above the bed of clay passing down into bedded shales the eight-foot section of 
* Brit. Assoc. Rep., 1916 (Newcastle), p. 206. 
+ The following slides in the Kidston Collection give a complete survey of this vertical section : — 
N 20, 2561 
N 19, 2429 
M 18a, 2560 
M 186, 2559 
L 17, 2558 
L 16, 2430 
IC 15, 2562 
I 14, 2435 
H 13, 2563 
G 12 , 2564 
F 11a, 2565 
F 116, 2556 
When a number of slides are mentioned, as in B 6 and 
E 10, 2566 
E 9, 2518 
D 8, 2543 
B 6, 2449, 2567, 2458, 2487 
A"2, 2499 
A'T, 2492, 2447, 2444, 2533, 2514, 2423. 
A'T, they are in descending order through the bed. 
