THE STEM 



97 



Fig. 113. — Ver- 

 tical section of corn- 

 stalk (reduced) : g, 

 groove ; c, cortex ; v, 

 fibrovascular bundles 

 mingled with paren- 

 chyma ; h, bud ; n, 

 node. 



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 the leaves ; 

 find their point of union with the stem; 

 with what part of it do they appear to be 

 continuous ? Has this anything to do with 

 the greater abundance of fibers near the epi- 

 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. 



III. 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 



