CHapter IV. 
THE STEM. 
The stem is, broadly speaking, a subsidiary organ 
of the plant, and serves rather to place other organs in 
positions in which they can best do their work than 
to perform a special function of its own. It forms 
an avenue of communication between the leaves 
and all other parts of the plant, and at the same time 
serves to spread out the leaves in the air and sunshine, 
and to display the flowers and fruit for the attraction 
of insects, birds and other animals. 
ARRANGEMENT OF TISSUES. 
In order to see exactly how the stem is able to act 
as a conducting channel it will be well to examine its 
structure. Cut sections of the bean stem (Fig. 56) as 
was done in the case of the root, being careful as 
before to keep both razor and material thoroughly wet. 
Place the sections on a piece of glass and hold them up 
to the light. With a good hand lens the cellular 
structure may be noted, though, of course, details will 
not be clear. The arrangement of the different tissues 
is, however, plainly exhibited. Inside the epidermis, 
whose presence may best be shown by tearing it from 
a piece of stem, is the cortex, in its outer parts con- 
taining chlorophyll, and therefore helping the leaves in 
their work. Inside the cortex is a circle of dark patches 
practically bisected by a complete ring of  pale- 
coloured tissue. The dark patches are the vascular 
bundles, and the pale tissue is the cambium. In each 
bundle, the part inside the cambium ring forms the 
wood while that on the outside constitutes the bast. 
The tissue between the vascular bundles forms the 
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