190 
Notes on Recent Literature. 
The most striking peculiarity of Adelophyton is perhaps the 
independence of xylem and phloem except in the leaf-traces, but the 
absence of any cauline xylem except the small internal compen¬ 
sation strand, and the central protophloem are highly peculiar. M. 
Bertrand remarks that the anastomosing phloem-strands, the 
structure of the individual phloem elements, the scalariform marking 
of the wood as well as the presence of highly developed “ apolar ” 
woody masses in the stem indicates a filicinean affinity ; the horse¬ 
shoe-shaped trace seems to point in the same direction. M. 
Bertrand does not offer any suggestions as to the phylogeny of this 
peculiar type of vascular structure ; the internal strand, however, 
is strongly reminiscent by its spiral course from leaf gap to leaf 
gap of the internal strands of polycyclic Ferns, especially of the 
single internal strand present in some of the simpler dicyclic forms. 
In the Ferns internal strands not uncommonly contribute to the 
leaf-traces, e.g., Matonla pectinata, Pteris aquilina , etc.; but in these 
eases they merely contribute to what appear to be, phyloge- 
netically, later complications of the trace. But if we suppose that 
a reduction of xylem were to take place in a dicyclic form with a 
single internal strand and that such reduction were to be continued 
until all the purely cauline portions of the external (primitive) 
xylem cylinder had disappeared, it is obvious that it would be 
advantageous for the internal strand which usually comes into 
contact with the edge of the leaf gap, and which may contribute to 
the elaboration of the trace, to fuse with the incoming woody 
masses of the traces. Mr, Tansley has pointed out “.., . that it 
is apparent that the primary stimulus to the development of an 
internal vascular system is the need for providing additional con¬ 
ducting or. water storing tissue at the leaf gap when the departure 
of the trace largely diminishes the conducting capacity of the stele 
above that point” (4). It would seem that conduction to the 
traces would, in the absence of cauline portions of the external 
cylinder, be best brought about by a connection of trace and 
internal strand, and that in Adelopyton Jutieri this has been effected 
not by the bending out of the internal xylem-strand but by the 
the inward penetration of the xylem only of the trace. Such 
a course of evolution would involve a considerable reduction of the 
xylem of a dicyclic form. It is therefore interesting to note that 
M. Bertrand considers that the aeriferous tissue of this fossil 
denotes a very damp medium, such as might cause reduction of the 
xylem ; he compares this tissue to that found in plants with the 
