THE STEM. 29 
We have now to deal with the structure of the stem, and this 
may be considered under the two headings of anatomy, which 
treats of so much as can be made out with the eye alone or by 
help of a lens, and histology, which goes into the finer details by 
employing a compound microscope. We may commence by an 
examination of sunflower and asparagus stems. 
Anatomy.—A good-sized example of a sunflower stem will be 
more or less cylindrical in shape, somewhat ridged, and studded 
with stiff hairs. If A 
an internode is cut 
across with a sharp 
knife, and the surface 
smoothed by a scalpel 
or razor, the three 
systems of tissue can 
be made out. There 
is first the hair-bear- 
ing epidermis, and 
some little distance 
within this a circle 
of small oval areas, 
separated by inter- 
spaces. These are the 
cut ends of the vas- 
cular bundles, and 
are best seen with a 
lens. The rest of the °¢ 
stem is made up of 
ground-tissue, which 
is divisible into a 
large white central 
part, pith or medulla ; 
another part, cortex, 
between the epider- 
mis and_ vascular 
bundles; and thirdly, 
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‘Ia. 5.—Diagrams of Anatomy of Vegetative Organs [after 
medullary rays, strips 
of tissue running be- 
tween the vascular 
bundles, and _ con- 
necting pith with cor- 
tex. If now a piece 
of the stem is halved 
Prantl). A. relation of stem and leaves; J. leaves ; b. 
buds; g.p. growing-point; v.b. vascular bundles. The 
double line on outside represents epidermis. B. origin of 
lateral roots as seen in longitudinal section of bean; v.c. 
vascular cylinder ; J.7. lateral roots; 7.c. root-caps. C, D. 
course of vascular bundles in stems of monocotyledon and 
dicotyledon. J. leaves; p. pith; co. cortex. E. piece of 
wood to show course of medullary rays ; m.7. rays ; as seen 
in a cross-section ; 7.2”. rays as seen in a radial section ; 
m.r”’, rays as seen in a tangential section. 
longitudinally (taking care to include a node, and to cut through’ 
the attachment of a leaf), and the pith carefully scraped away 
