116 PRACTICAL COURSE IN BOTANY 
the upward flow takes place through the cells of the xylem, 
which contain no protoplasm (116), this explanation is in- 
adequate, and we must be content, in the present state of our 
knowledge, to accept the fact as one which science has yet to 
account for. 
Practical Questions 
1. Why will a leafy shoot heal more quickly than a bare one? (125, 
126; Exp. 58.) 
2. Why does a transverse cut heal more slowly than a vertical one? 
(126, 127.) 
3. Why does a ragged cut heal less rapidly than a smooth one? 
4, Why does the formation of wood proceed more rapidly as the amount 
of water given off by the leaves is increased? (126; Exp. 59.) 
5. Why do nurserymen sometimes split the cortex of young trees in 
summer to promote the formation of wood? (116, 118.) 
6. What is the advantage of scraping the stems of trees? 
7. Explain the frothy exudation that often appears at the cut ends of 
firewood, and the singing noise that accompanies it. [120, 124 (2).] 
8. Of what advantage is it to high climbing plants, like grape and 
trumpet vine (Tecoma), to have such large ducts? (111, 116, 122.) 
9. Why is the process of layering more apt to be successful if the shoot 
is bent or twisted at the point where it is desired to make it root ? (127; 
Exps. 60, 61.) 
10. Why do oranges hecome dry and spongy if allowed to hang on the 
tree too long? (72, 126; Exps. 60, 61.) 
11. Why will corn and fodder be richer in nourishment if, at harvest, 
the whole stalk is cut down and both fodder and grain are allowed to 
mature upon it? (126, 127; Exps. 60, 61.) 
12. Is the injury done it plants by freezing due, as a general thing, 
to mechanical, or to chemical action? (33.) 
13. Why in pruning a branch is it best to make the cut just above a 
bud? (Exps. 60, 61.) 
14. Why is the rim of new bark, or callus, that forms on the upper side 
of a horizontal wound, thicker than that on the lower side? (126, 127; 
Exps. 60, 61.) 
15. Why is it that the medicinal or other special properties of plants 
are found mostly in the leaves and bark, or in the parts immediately 
under the bark? (120, 126.) 
16. Why does twisting the footstalk of a bunch of grapes, just before 
ripening, make them sweeter? (127.) 
