26o 
ERNST F. ARTSCHWAGER 
C. Longitudinal section of xylem showing both types of vessel. 
D. Radial section of stem showing size and longitudinal course of the phloem. 
E. Radial section of primary xylem showing spiral and ringed elements. 
F. Radial section of phloem showing the sieve tubes with companion cells and phloem 
parenchyma. 
G. Radial section of xylem showing (from left to right) fibers, vessels, and conjunctive 
tissue. 
Plate XVII 
A. Cross section of part of young stem showing the appearance of an extrafascicular 
cambium above a phloem group. 
B. Cross section of a more mature stem showing the same condition as in u4. Druse 
of calcium oxalate in cell of cortex. 
C. Section of primary bundles of stem. Above the bundles an extrafascicular cambium 
has developed which is several rows wide. 
D. Cross section of young stem showing several primary bundles and the first zone of 
thickening. 
E. Section of vascular strand initial. Extrafascicular cambium has developed above 
the newly formed phloem group. 
F. Section through annual zone of growth showing the development of an initial strand 
of phloem. 
