THE STEM 97 
with a hand lens. Observe that it is composed of a number 
of oblong cells packed together like bricks in a wall. These 
are filled with protoplasm and cell sap, and constitute what is 
known to botanists as the parenchyma or 
fundamental tissue from which all the other 
tissues are derived. Apply the iodine test ; 
in what parts does starch occur most abun- 
dantly ? 
Draw out one of the woody threads run- 
ning through the pith. Break away a bit of 
the epidermis, and see how very closely they 
are packed on its inner surface. Trace the 
course of the veins in the bases of theleaves; pig. 113. — Ver- 
find their point of union with the stem; tical section of corn- 
with what part of it do they appear to be ee 
continuous? Has this anything to do with Sbrovaseulat bundles 
ingled with paren 
the greater abundance of fibers near the epi- chyma; }, bud; 2, 
dermis? Can you follow the fibers through ™°** 
the nodes, or do they become confused and intermixed with 
other threads there? (If a stalk of sugar cane can be 
obtained, the ring of scars left by the vascular bundles as 
they pass from the leaves into the stem will be seen beauti- 
fully marked just above the nodes.) 
If there is an eye or bud at the node, see if any of 
the threads go into it. Can you account now for the de- 
pression that occurs in the internode above the eye? 
Make drawings of both cross and vertical sections, showing 
the points brought out in your examination of the cornstalk. 
111. The vascular system. — To find out the use of the 
threads that you have been tracing, examine a piece of a 
living stem that has stood in red ink for three to twenty-four 
hours. Notice the course the coloring fluid has taken; what 
would you infer from this as to the use of the woody fibers? 
These threads constitute what is called the vascular system 
of the stem, because they are made up of vessels or ducts, 
along which the sap is conveyed from the roots to the leaves 
mista 
