360 = Structural and Physiological Botany. on ea 
branched off from the stem together with the leaves at the . | 
time when the latter first began to be formed. The circum-— 
stance that branches of the vascular bundles which pass from 
the stem into the leaves—the so-called leaf-traces—do not | 
bend into the leaf immediately that they branch off, but 
often remain as a separate bundle running through a con- 
siderable length of the stem, causes the appearance of the 
vascular-bundle-system to be often very complicated, es- 
pecially when several leaf-traces which have branched off 
from different cauline bundles enter the same leaf. 
In Fig. 473 we have a diagrammatic representation, after Nageli; 
of the course of the vascular bundle through twenty-two internodes of 
22 the apex of the stem of /deris 
x | + erecta 231 | amara. Each of the leaves 
2 ean, | | has a vascular bundle, the 
; ; 
3) 
6 
leaf - traces of which are 
drawn as far as the points 
of attachment of the leaves. 
The internodes are separated 
by the horizontal lines. Each 
leaf-trace appears, therefore, 
when seen in transverse sec- 
tion, to run as a separate 
bundle through ten or eleven 
internodes, and invariably 
unites with the bundle from 
the fifth leaf below; thus the 
fifth with the tenth, the tenth 
with the fifteenth, &c. If 
transverse sections are made 
through the internodes, the 
number of vascular bundles 
which will be found exposed 
Fic. 473.—Diagrammatic representation of the on each section is 1ndicated _ 
che ca ae bundles in /berzs amara by the number given on the’. 
left-hand side of the figure. 
In the leaf-trace of the twenty-second leaf are found fully developed 
vessels, the probable subsequent course of which is indicated by the 
dotted line. | 
The course of the vascular bundles is not, however, always 
