52 
Scott. — On a Palaeozoic Fern , the 
The conclusions as to the aphlebiae are — 
(1) that they are borne on all parts of the stem, without any special 
relation to the leaf-base ; 
(2) that their strands come off from the leaf-trace, both below and above 
its separation from the stele ; 
(3) that the protoxylem of the strand is central ; 
(4) that the strand divides into two or three branches when the aphlebia 
becomes free. 
The Roots. 
Adventitious roots are not very numerous in the Shore specimen ; they 
are better shown in the second Williamson specimen ; the illustration on 
PI. V, Fig. 14, is from a section of this specimen from the Manchester 
Museum, kindly lent by Prof. F. E. Weiss. There appears to be no 
difference among the different specimens in the way the roots are borne. 
They spring laterally, as a rule, from the arms of the stele, the base of the 
root-stele occupying in some cases about half the length of the arm (Fig. 14). 
In the Shore specimen, where the peripheral loops are evident, it is seen 
that they contribute to the elements of the root-xylem (see above, p. 48). 
The root-steles are given off on both sides of the stelar arm ; sometimes 
two roots are opposite, in about the same plane. They arise from the arms 
at different levels, but I have not found them in connexion with the leaf- 
trace when free from the stele. They pass out horizontally. 
As regards the structure of the root the evidence is still imperfect, for 
I have not yet seen a root in transverse section showing its connexion with 
the stem. In the Shore sections there are two or three roots near the stem 
which probably belong to it. They are about 1 mm. in diameter and diarch, 
with a very bulky xylem-plate, elliptical in transverse section. The cortex, 
if complete, is rather narrow, and sometimes has a pentagonal outline. 
Quite similar roots are also associated with the second Williamson 
specimen. 
The Williamson Specimens. 
The general description of the structure given in the earlier part of the 
paper is based essentially on the later Williamson specimen, the most perfect 
known before the discovery of the Shore fossil, and superior even to the 
latter in certain respects. 
The eight sections of this specimen which I have seen are enumerated 
on p. 39. I have taken some pains to determine their correct order, which, 
from below upwards, appears to be as follows : 
1. ( 7 ) Williamson 1919 D. 
2. (8) „ 1919 B. 
3 - ( 1 ) » I 9 I 9 C. 
4. (2) „ 1919 A. 
