12 BOTANICAL GAZETTE [JANUARY 
is very generally absent in the strands which conduct the assimi- 
lates from the leaf into the stem. The conducting efficiency of 
the foliar trace would obviously be considerably reduced were part 
of the assimilates to be used in the growth of the bundles of the 
foliar traces instead of being transferred intact to storage in the 
stem or seeds. High conductive efficiency, notably correlated in 
herbs with the assimilative productiveness of the leaf, as will be 
pointed out later, is in general associated with the loss of cambial 
activity in the foliar traces as they enter the cylinder of the stem. 
In the root the most obvious interpretation of the absence of 
secondary woody growth is the unfavorable effect that a jacket of 
secondary elements would have on the ease of penetration of the 
water absorbed by the root hairs into the water-conducting tissues 
of the central cylinder. Since the essential conditions of the loss 
of a cambium are different in stem and root, it is clear that both 
may not present the feature of the loss of secondary activities in 
their fibrovascular structures at the same time. In other words, 
the stem may be herbaceous and the root woody; or vice versa, the 
stém may be woody and the root herbaceous. The former con- 
dition is well exemplified by certain species of Papaver, while 
Aster furnishes examples of the latter. 
We may now turn to a type which is still more delicate in its 
herbaceous texture than are either Aster or. Helianthus. Like 
the sunflower, the buttercup often serves as an example of the 
herbaceous type in laboratory exercises, and for that reason it is 
chosen in this connection, as illustrating a common and easily 
obtained plant. Fig. 22 illustrates the organization of a small 
stem of Ranunculus acris in the region of the branching node. 
The larger cylinder below represents that of the main axis, while 
the branch cylinder is smaller and appears above. Inclosing the 
branch and fused with it is the base of a leaf, in which may be 
distinguished 5 fibrovascular bundles, the leaf traces. As the 
cylinders of axis and branch come together, the phloem of their 
uppermost and lowest bundles respectively face one another. In fig. 
23 is shown a somewhat lower plane of section in a rather larger 
stem than that illustrated in fig. 22. Here the union of secondary 
and main axes has taken place with interesting results. In the 
