388 EQUISETALES 
the number of the tracheides in these varies in different species 
(Fig. 211 8B, D, F). It will be shown that these are not directly con- 
tinuous with the xylem of the leaf-trace. The phloem lies between them, 
and consists of sieve-tubes and parenchyma. 
If the vascular tissues be followed onwards into the nodes, the structure 
there displayed will give ground for a proper understanding of the inter- 
nodal strands. Hitherto it has been customary to treat these as integral 
“vascular bundles” of the collateral type, comparable with the leaf-trace 
bundles of Phanerogams: they have been assumed to enter the axis from 
the leaves as integral bundles, and to pursue their course down one 
internode, maintaining their identity as 
integral bundles to its base: there 
each was held to bifurcate, and the 
shanks to affix themselves right and 
left.on the nearest lateral bundles 
which pass in at the lower node. This 
was the scheme contemplated by De 
Bary ;! but it is a scheme characteristi- 
iM cally Phanerogamic, and it has always 
presented difficulties of comparison with 
other Pteridophyte-types. An advance 
to a more intelligible view, based upon 
IK K more exact analysis of the nodal 
structure, has been the result of the 
investigations of Gwynne-Vaughan,? to 
whom I owe the use of hitherto un- 
Fic. 212. published drawings, as well as the 
Diagram constructed by Mr. Gwynne-Vaughan description which follows. He found 
cysten of guisrure. ‘Thedoed lines dicate that in £. Zelmateja, of the three 
aotinunes lines fadieate thecudline stands, "* strands of xylem present in each bundle 
of the internode the carinal strand alone 
passes out at the node as a leaf-trace. The two lateral strands join on 
to the xylem of the nodal ring, where the xylem is much more amply 
developed than in the internode, and even shows some slight degree of 
secondary increase.? In certain species (4. Aiemale, and better still in 
£. giganteum) the lateral strands of the internodal bundles may be traced 
as externally projecting ridges over the nodal xylem into the internode 
above. In passing through the node they diverge from one another, so 
that in the internode above they are found on the adjacent sides of two 
different bundles. At the node above they approach each other, and in 
the next internode they both occur in the same bundle once again. The 
x 
bs 
Saas 
S 
4 
ee 
a 
Pee pene ete 
SSS oS 
>= So eet. 
ss <= = ee 
SSS Se 
> SS See = 
s 
4 
eo 
SSSs SoS 
>= <- 
> - - 
x 
Y 
x 
Y 
4 
SsSo 
f 
‘ 
V4 
1 
t 
t 
‘ 
‘ 
1 Comp.-Anat., pp. 279 and 327. 
2?Gwynne-Vaughan, Refort Brit. Ass., Glasgow, 1901, p. 850; also Anz. of Bot., 
1901, Pp. 774- 
°> Cormack, Aznals of Botany, vii., p. 63. 
