18 BOTANICAL GAZETTE [JANUARY 
infranodal region of the common garden bean. Since the lower 
part of the aerial stem is represented, the cylinder is somewhat 
thick and woody, as well as round in form. A leaf trace occupies 
the central region of the figure, and it is clearly marked by the 
absence of the dark cambial zone, which marks the stem bundles 
on either side. It is evident that absence of secondary activity 
is a feature of the leaf trace in a form which for many years has 
served in the laboratory for an example in studying the anatomy 
of the herbaceous dicotyledonous stem. As a further illustration 
the aerial axis of the common red clover (Trifolium pratense) may 
be used. Fig. 42 makes clear the conditions found in the nodal 
region of this species. A well marked black band indicates the 
cambial activity of the bundles of the stem proper. In the median 
region appears a leaf trace which is quite conspicuously without 
cambial activity, and in this respect presents a marked contrast 
with the cauline bundles which are adjacent to it on either flank. 
These illustrations, which might be indefinitely multiplied from 
the common leguminous types, clearly show that in this group the 
tendency toward the elimination of cambial activity in the leaf 
trace makes itself obvious. 
The garden poppy will supply an example from another and 
somewhat distant group. In fig. 43 is shown the region of the 
node in the annual garden poppy of hybrid origin (Papaver 
cross). The foliar traces in many cases in this genus enter the 
stem as double strands. One of these pairs appears in the center 
of the figure, and it can easily be seen that its constituent strands 
are without the secondary activity due to the presence of the 
cambium, exemplified in the cauline bundles on either side 
. of the foliar pair. Fig. 44 shows a total transverse section of 
the stem of the wild morning glory (Convolvulus sp.). On the 
upper side of the cylinder is shown a broad arc breaking away 
from the fibrovascular ring. This is the leaf trace of the leaf 
attached to the next node above. Nearly opposite, but some- 
what obliquely placed, is a trace of a still higher leaf. It is clear 
that the foliar traces show a considerably less degree of second- 
ary growth than is found in the fibrovascular tissues of the stem 
proper. 
