STEMS OF MONOCOTYLEDONS 151 



there ? (If sugar cane is used for this study, the ring of 

 scars left by the vascular bundles as they pass from the 

 leaves into the stem will be seen beautifully marked just 

 above the nodes.) 



If there is an eye or bud at the node, look and see if 

 any of the threads go into it. Can you account now for 

 the depression that occurs in the internode above the eye 

 or bud ? 



Make drawings of both cross and vertical sections show- 

 ing the points brought out in your examination of the corn- 

 stalk. 



214. The Vascular System. — To find out the use of 

 the threads that you have been tracing, examine a piece 

 of a living stem of wild smilax or other monocotyledon 

 that has stood in red ink for three to twenty-four hours. 

 (If the specimen stands in the coloring fluid too long the 

 dye will gradually percolate through all parts of it. If 

 this should be the case, look for the lines that show the 

 ink most plainly.) Notice the course the coloring fluid 

 has taken ; what would you infer from this as to the 

 office of the woody fibers ? 



These threads constitute what is called the vascular 

 system of the stem, because they are made up, to a large 

 extent, of little vessels or ducts, along which the sap is 

 conveyed from the roots to the leaves and back from the 

 leaves to the root and stem after it has been elaborated into 

 food. They are, so to speak, the water pipes that supply 

 the leaf community with the liquid nourishment which it 

 works up into food during the process of photosyn- 

 thesis (Sec. 24). 



215. The Stem as a Water Carrier. — We see from this, 

 that the stem, besides serving as a mechanical support, 

 is the natural line of communication between the roots, 

 where the raw material for feeding the plant is gathered, 

 and the leaves, where this material is manufactured into 

 food. After the sap is there elaborated and the surplus 

 moisture given off by transpiration, the nourishment is 



