1922] BROWNE—EQUISETUM 463 
posing them are reticulately thickened. In nodes of the fertile 
stem of E. maximum I was able to trace the forking of the persistent 
protoxylem, the divergence of the forks, and their passage into 
separate though neighboring bundles. Each of the newly con- 
stituted bundles thus contained two small groups of protoxylem, 
but in no case could a connection between these forks and the 
protoxylem of the internode above be observed; they seemed 
always to die out. 
As we are dealing in Equisetum with plants showing a reduced 
vascular system, it is probable that the dying out of part or all of 
the protoxylem of one internode without coming into connection 
with the protoxylem of the next is a derivative character, and that 
the course of the protoxylem described for E. giganteum is primitive 
within the genus. In this connection it may be pointed out that 
in the fertile stem of E. maximum, although the bundles are of 
much the same width as those of the large young axis of E. giganteum 
described in this paper, the height and the radial extent of the nodal 
wood of the latter, even in its young condition, were nearly twice 
as great as the height and depth of the nodal wood at the nodes of 
the fertile stems of E. maximum studied. Moreover, it has been 
shown (4) that the cone of E. maximum has a much reduced 
vascular system. 
It is possible that at the nodes of the sterile stems of E. arvense 
and E. maximum none of the protoxylem, at least in typical cases, 
persists above the departure of the tracheids of the trace. This 
appears to be the view of JEFFREY and Miss BARRATT. On the 
other hand, Quéva’s figures seem to show that sometimes at least 
the protoxylem persists, at any rate for some distance above the 
departure of the tracheids to the trace. Such protoxylem as per- 
sists at the node is small in amount and often inconspicuous, so 
that in many cases it may well have passed unnoticed. When, 
however, as in E. hiemale, the protoxylem disappears completely 
at the level of the departure of the tracheids of the trace, this 
would seem to be due to a further reduction along the lines exempli- 
fied at the nodes of the fertile axes of E. debile and E. maximum. 
Passing from the consideration of the protoxylem to that of the 
metaxylem, we again meet with a conflict of evidence. In 1890 
