1922] BROW NE—EQUISETUM 451 
elements, constituting the metaxylem of the trace, are more numer- 
ous than the protoxylem elements that pass out into the leaf. 
The metaxylem of the trace detaches itself from the nodal tracheids 
of the bundle before the phloem of the trace is set free from that 
of the axis. The endodermis of the bundle is beginning to bulge 
out somewhat opposite the trace that is preparing to depart. 
During its passage through the bundle (fig. 1, stage 7) the proto- 
xylem of the trace is very clearly distinguishable under the micro- 
scope from the metaxylem, because, in a transverse section of the 
axis, the protoxylem running out from the carinal canal is cut 
almost longitudinally, while the metaxylem, some of the elements 
of which are not much larger, is moving so slowly and steeply 
upward and outward that its tracheids are cut almost transversely. 
When the junction of the protoxylem with the metaxylem has been 
effected, the tracheids of the former bend sharply upward and 
pursue the same steeply oblique course as the elements of the 
metaxylem. At this level the protoxylem is again disorganized, 
so that the trace contains a small protoxylem canal. This at 
first lies at the inner edge of the wood, but soon becomes somewhat 
internal in position, so that the xylem of the trace becomes mesarch 
almost at once. Before the trace is set free its protoxylem has 
assumed an approximately central position. 
When the protoxylem has passed through the parenchymatous 
gully, two to four rows of parenchymatous cells, resembling those 
occurring below and on the sides of the departing protoxylem, 
are found above the latter. Thus the protoxylem runs through the 
nodal tracheids surrounded by a sort of parenchymatous sheath.’ 
Immediately above the cells of this sheath nodal tracheids again 
form, leaving, however, a parenchymatous notch opposite the 
point of departure of the xylem of the trace. 
Concurrently with the appearance of these tracheids the carinal 
canal becomes much narrower radially, and frequently contains 
a certain number of somewhat torn tracheids. It is usually at 
this stage that the nodal xylem of adjacent bundles becomes con- 
fluent. This union may take place in two ways. Where (as was 
2 Such a parenchymatous gully has also been observed at the nodes of E. palustre 
and E. hiemale. 
