452 BOTANICAL GAZETTE [JUNE 
the case at the points of junction of by far the greater number of 
bundles) the stele of a branch was inserted on the axial stele, 
the bundles of the latter first became united by their outer ends. 
Here the nodal xylem unites to form a sort of arch (fig. 2, stage 8). 
The curve of this arch constitutes the outer and lower half of the 
continuous hollow central cylinder of the branch at its oblique 
insertion on the axial stele. At a slightly higher level the more 
internal nodal xylem also becomes confluent, usually at a point 
about halfway between the periphery of the nodal xylem and its 
inner edge (fig. 3, stage 9g). The tracheids at and near this junction 
Fic. 2.—Stages 8a and b: x.tr xylem of trace; br.x.tr, xylem of branch trace; 
other lettering as in fig. 1; XX about 120. 
mark the insertion of the inner higher portion of the continuous 
ring of wood of the branch. At this level, however, the lower 
outer edge of the siphonostele is no longer visible, so that no 
single section shows the complete siphonostele of the branch and 
the continuity of its “pith” with that of the stem. Where no 
branch is given off, the bundles become laterally united in their 
middle regions by a narrow neck of xylem, as shown on both sides 
of the bundle in fig. 2, stage 8a. This neck of xylem rapidly 
thickens. The special endodermes lie outside the nodal tracheids, 
and their fusion precedes the junction of the xylem of adjacent 
bundles.* As we pass upward certain cells on the adjacent sides 
3 For a fuller description of the insertion of the vascular system of the branch on 
that of the stem, see PritzER (12, pp. 329-330, fl. 20, figs. 19, 20, 23)- 
+A fuller account of the behavior of the special endodermes at the nodes will be 
found in PritzEr’s (12) description of their distribution at the nodes of E. limosum 
and E. litorale. 
