Oct., 1921] 
BECHTEL FLORAL ANATOMY OF URTICALES 
into three strands (fig. 7, m), and fifty microns above the latter section these 
strands are well away from the stele and a second trace passes off lateral to 
the first (fig. 8, m}) and behaves exactly like the posterior except for the 
subsequent branching. Twenty microns above the last section a trace, in 
appearance like the others, passes out of the stele opposite the second trace 
(PI. XV, fig. 9, w?) ; but twenty microns above this section, as represented in 
figure 9, the inner portion of this trace appears as a very faintly lignified 
vessel (figs. 10, 11, w^), similar in origin and position to those supplying 
stamens with other lobes. This weak strand aborts seventy microns above 
its origin. It is clearly the supply to a suppressed stamen. The remaining 
lateral traces pass off right and left (PL XV, figs. 11-13) in close succession. 
The supplies to the anterior lobe and to the two anterior-lateral lobes appear 
to pass off simultaneously (PI. XV, figs. 14-15, w^ w^ m^), and all traces sep- 
arate into staminal and perianth traces coincident with their departure from 
the stele. This fact is revealed also by longitudinal sections (PI. XV, fig. 3, h) 
When the strands to the perianth and to the stamens are definitely dif- 
ferentiated, such a distinct regional differentiation of tissue arises that the 
stamen supply is demarked from the adjacent tissues, forming what may be 
designated as a staminal cylinder (PI. XVI, figs. 16, 17, c). This cylinder 
persists until the stamens become free from the perianth. At this level the 
branching of the perianth strands is usually complete; the posterior and 
anterior separate into two or three strands; the lateral strands rarely 
separate or branch (PI. XVI, fig. 18, w, m^). 
With a knowledge of the gross morphology of the U. americana flower, 
the above described structure is really what might be expected. However, 
anatomical study reveals additional abortive bundles present in the anterior 
half of the flower. These bundles arise immediately within and above the 
bundles to the stamens and alternate with them. They appear in the same 
sequence as the bundles to the perianth parts and to the stamens and are 
evident in transverse sections as soon as the bundles to the stamens are 
distinctly established in the ''cortical" region (PI. XV, figs. 11-14, d^, 
. . . d^; fig. 3, c^^; fig. 4, d"^, d^). These abortive bundles occurring above 
the bundles to the stamens and below the supply to the carpels show no 
lignification. They are characterized by cells of small size and by a tissue 
organization more close than that of the surrounding tissue. The origin 
of these strands from vascular bundles and the reseml^lance of the com- 
ponent cells to those of young or weakly developed bundles render their 
bundle nature undoubted. The centrally located cells of these demarked 
regions are very small and often exhibit the appearance of being crushed. 
They thus suggest the appearance of protoxylem as often seen in mature 
tissue. These abortive bundles extend upward approximately 150 microns. 
The question arises, are these the vestigial parts of suppressed stamens? 
There seems to be no alternative conclusion. The same phenomenon is 
found also with the strands leading to the carpels higher up in the floral 
axis (PI. XVI, fig. 16, e] PI. XV, fig. 4, e) as discussed below. 
