THE WORK OF LEAVES 93 



EXERCISE 31 



Object. — To determine how much food is manufactured 

 in the leaves. 



Procedure. — Cut into very fine pieces one hundred 

 grams of potato, grass, apple or any grain. Weigh 

 again after cutting to make sure that your original weights 

 are accurate. Set the pan or dish containing your material 

 on the back of the stove or in an oven. When perfectly 

 dry but not burned, weigh again. 



Put the dried material into a dish which will withstand 

 heat, and carefully burn it over a hot fire. When nothing 

 but white ashes remains, take the final weight. 



Conclusion. — How much water did the material which 

 you used contain? Where did it come from? Will it 

 get back to the soil again ? If so, how? How much food 

 material and how much ash did the substance which 

 you used contain? Where did each come from? What 

 element came from the soil but escaped into the air? 

 Give two reasons why cornstalks and straw should not 

 be burned. (Sections 4 and 68.) How do your results 

 compare with those of others who used other material? 

 Why do grains produce more flesh and energy in animals 

 than the same weight of green forage, potatoes, beets or 

 other root crops? 



69. The Water given off by Leaves. — The minerals 

 which a plant takes in are really received in a very weak 

 solution. In other words, a great deal of water is ab- 

 sorbed to get a small amount of phosphorus, potassium 

 or any other element required from the soil. The excess 

 of water must escape, and it does so through the leaves. 

 On the under side of leaves, and to a limited extent on 

 the upper side also, are found numerous tiny openings, 

 called stomata. These stomata are guarded on either 



