MOVEMENT OF WATER THROUGH THE STEM 163 



pressure affects the free contents of these parts, just as 

 we may sink a water pipe into the ground and at the same 

 time force the water upward through it. 



231. Direction of the Current. — Remove a ring of the 

 cortical layer from a twig of any readily rooting dicoty- 

 ledon, being careful to leave the woody 

 part with the cambium intact. Place 

 the end below the cut ring in water, as 

 shown in Figure 307. 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 Section 221 .? 



Next prune away the leaves and pro- 

 tect 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 most abun- 

 dantly from above or below the decorti- 

 cated ring .' 



These experiments show that the up- cortical tissue: a, level 



, . ^ ^ , of the water; ^, swell- 



ward movement of crude sap toward the jng formed at the 

 leaves is mainly through the ducts in "??«"■ denudation; c, 

 the woody portion of the stem, while the 

 downward flow of elaborated sap from the leaves takes 

 place chiefly through the soft bast and certain other 

 vessels of the cortical layer. 



232. Ringing Fruit Trees. — This explains why farmers 

 sometimes hasten the ripening of fruit by the practice of 

 ringing. As the food material cannot pass below the 

 denuded ring, the parts above become gorged and a pro- 

 cess of forcing takes place. The practice, however, is 

 not to be commended, except in rare cases, as it generally 

 leads to the death of the ringed stem. The portion below 

 the ring can receive no nourishment from above, and will 

 gradually be so starved that it can not even act as a carrier 

 of crude sap to the leaves, and so the whole bough will 



307. — A twig which 

 had been kept stand- 

 ing in water after the 

 removal of a ring of 



