THE STEM AND ITS FUNCTIONS 115 



371. How is it possible for a tree which is "hollow-hearted" to thrive 

 and grow? 



372. In tapping maple trees for sap, it is necessary to run the tap into 

 the tree for only a very short distance. Why? 



373. Cut flowers will keep fresh longer if the cut ends of their stems 

 are trimmed off daily; if, after cutting, the ends are placed in boiling 

 water for a moment ; if the water in which the flowers stand is frequently 

 changed, or if a little salt is added to the water. Explain how it is that 

 these various procedures tend to effect the desired result. 



374. How would you prove that manufactured food travels in the 

 bast? 



375. Why will a girdled tree ultimately die? 



376. Why is the chestnut-bark disease, which attacks only the outer 

 bark, cortex and bast, so fatal to chestnut trees? 



377. Why is a wire ring or other tight metal band around a tree 

 trunk likely to injure the tree severely in time? 



378. If a trunk is bound tightly with wire, a swelling of the tissues 

 finally appears above the wire. Explain. 



379. In propagating a plant by "layering," a gardener bends a branch 

 down to the ground and covers a portion of it with earth in order that 

 it may root at that point. Roots will grow much better if the stem is 

 bent or twisted strongly at the point where roots are desired. Why? 



380. In "Chinese" layering, a ring of bark is cut off around the stem, 

 as far in as the wood, and that part of the stem is covered with moist 

 moss. Roots eventually appear just above the ring, but not below it. 

 Explain. 



381. In order to obtain very large fruits for exhibition, growers some- 

 times "ring" a fruit-bearing branch some distance below where the 

 fruit is growing. Explain why this has the desired result. 



382. What foundation in fact is there for the old belief that by 

 driving nails into the trunk of a plum or a peach tree, larger fruit will 

 be obtained? 



383. If a tree is "girdled" while its leaves are out, will the leaves wilt 

 or not? 



REFERENCE PROBLEMS 



49. Give an example of a stem which has assumed some of the functions 

 of a leaf; of a root. 



