1921] JEFFREY & TORREY—HERBACEOUS ANGIOSPERMS 19 
An examination of many nodes in herbaceous Dicotyledons has 
made it clear that there is a strong tendency for cambial activity 
to disappear in the leaf traces as they enter the cylinder of the 
stem. Even when the foliar trace does not intermit its secondary 
growth, there is always a considerable reduction of activity in this 
respect. This phenomenon, in fact, is not confined to Dicotyledons, 
but is also exemplified in Gymnosperms, both living and extinct, 
‘ and in Cryptogams where secondary woody tissues are developed. 
There is an obvious advantage to the plant in the elimination or 
reduction of cambial activity in the foliar strands, since the food 
materials elaborated in the leaves are thus more certainly assured 
of transfer, without essential loss, to the storage regions of the 
stem. In the case of the herbaceous Dicotyledons, however, the 
much greater degree of assimilative activity causes so great an 
emphasis of the limitation of cambial activity in the leaf traces 
that in a large number of cases it disappears altogether. This 
feature, together with the usual multiplication of leaf traces in 
the more pronounced herbs, has produced in extreme instances 
among the Dicotyledons conditions which are not essentially 
different from those obtaining in the anatomical organization of 
the Monocotyledons. 
In text fig. 1 is shown a stereodiagram of the stem of Helianthus 
in the region of a node. The node chosen is neither from the . 
extremely upper region of the aerial stem, nor from its stout woody 
ase. There are six leaf traces present, three facing, and three 
on the opposite side of the stem. Each trio of traces belongs to 
one of the opposite leaves. On the remote side the lateral traces 
are represented as passing into the leaf base, while the median is 
still in the axis. The nearer aspect of the stem is deprived of its 
superficial tissues, so that the relation of the traces to the organiza- 
tion of the wood may easily be seen. In the transverse aspect each 
leaf trace is clearly subtended and flanked by the storage tissues 
of the foliar rays. As the leaf rays descend in the stem they fork 
as a result of the intrusion of a median tongue of wood into the 
ray from below. Each foliar strand in the not too slender axis of 
Helianthus is accordingly related to a foliar ray which subtends it 
radially and at the same time accompanies it on either flank. 
