82 BOTANY: PRINCIPLES AND PROBLEMS 



256. Compare in detail the leaf of a green plant with a manufacturing 

 establishment. 



257. From the point of view of living things, which do you think are 

 the three most important chemical elements? Why? 



258. Which do you think would be worse for a tree, the loss of half of 

 its branches by an ice-storm or of all of its leaves through an insect 

 attack? Explain. 



Note. — By the term dry weight is meant the weight of all the material 

 in a given body except its water. It is usually determined in the labora- 

 tory by drying the material in an oven at about 100° C. 



259. Would the dry weight of a leaf be greater in the morning or in 

 the following evening? Why? 



260. Will seedlings grown in the dark increase in actual weight? 

 in dry weight? Explain. 



261. The leaves of parasitic plants are often very small. Explain. 



262. How do submersed water plants carry on photosynthesis? 



263. Give at least three reasons why trees often fail to thrive in a city. 



264. From your knowledge of plants, do you think that they need a 

 rest at night, or would they thrive continuously if the light were 

 continuous? 



265. Some crops produce a much larger amount of dry weight per 

 acre than others. Explain how this can be. 



266. The potato beetle does not attack the potato tuber, but eats 

 only the foliage of the potato plant. Why does it harm the crop? 



267. Why does repeatedly cutting off their tops finally kill persistent 

 perennial weeds? 



268. If a man wants to clean out suckers and low shrubs from pasture- 

 land, should he mow them down in summer or in winter? Why? 



269. Is there any basis in fact for the belief held by some farmers 

 that there is one particular day in summer when suckers and brush 

 should be cut down, if you want to kill them off? 



270. Which will give better and larger flowers the next season, tulip 

 bulbs which are pulled up immediately after flowering or those left in 

 the ground until after the leaves have withered? Why? 



271. Why should a new field of asparagus not be harvested until two 

 or three years after the young plants have been set out? 



