THE STEM 



113 



Experiment 59. What becomes of the water that goes into the 

 LEAVES ? — Cover the top of the vessel containing the leafy twig used in the 

 last experiment with a piece of card- 

 board, having first cut a slit in one side, 

 as shown in Fig. 128, so that it can be 

 slid into place without injuring the 

 stem. Invert over the twig a tumbler 

 that has first been thoroughly dried, 

 and leave in a warm, dry place. After 

 an hour or two, what do you see on the 

 inside of the tumbler ? Where did the 

 moisture come from ? 



Experiment 60. Through what 



PART of the stem DOES THE SAP FLOW 



UPWARD ? — Remove a ring of the cor- 

 tical layer from a 

 twig of any readily 

 rooting dicoty], 

 such as willow, 

 being careful to 

 leave the woody 



part, with the cambium, intact. Place the end beloio 

 the cut ring in water, as shown in Fig. 129. The leaves 

 above the girdle will remain fresh. How is the water 

 carried to them? How does this agree with the 

 movement of red ink observed in 115 and 122? 



Experiment 61. Through what part does the 

 SAP COME DOWN ? — Ncxt pruue away the leaves and 

 protect the girdled surface with tin foil, or insert it 

 below the neck of a deep bottle to prevent evaporation, 

 and wait until roots develop. Do they come more 

 abundantly from above or below the decorticated 

 ring? 



Fig. 128. — Experiment showing 

 that moisture is thrown off by the 

 leaves of plants. 



Fig. 129. —a 

 twig which had been 

 kept standing in 

 water after the re- 

 moval of a ring of 

 cottical tissue : a, 

 level of the water ; 

 b, swelling formed at 

 the upper denuda- 

 tion ; c, roots. 



124. The three principal functions of the 

 stem are : — (1) to serve as a mechanical sup- 

 port and framework for binding the other 

 organs together and bringing them into the best attainable 

 relations with light and air ; (2) as a water carrier, or pipe 

 line, for conveying the sap from the roots to the parts where 

 it is needed ; and (3) as a receptacle for the storage of foods. 



