STUDY OF FOODS 



33 



secure their carbon through their leaves, which absorb the 

 gas from the air.) From your observations can a plant 

 live indefinitely on water alone? 



B. Seal the growing seedling of A to the cork with melted 

 paraffin wax, cover the upper part of the seedling with a 

 test tube, and seal the edges of the tube to the cork. Does 

 the plant continue to live? (Plants can not live without 

 air.) What collects on the inside of the tube? What evi- 

 dence have you that a plant gives off water? 



C. Prepare a third and a fourth seedling as in A. In one 

 bottle put some nutrient solution made without the potas- 

 sium nitrate, and in the other the normal solution. Which 

 seedling lives longest? (To support life, one food required 

 by plants is some nitrogen salt like potassium nitrate.) 



D. Prepare a fifth seedling as in A, using a nutrient so- 

 lution with only the ferric chloride omitted. After several 

 weeks, notice the effect on the color of the plant. 



XX. NUTRIENTS PRESENT IN COMMON FOODS. 



Apparatus. Meat, flour, milk, parsnip, lettuce, peanuts, and the 

 necessary materials for the tests described in Exs. XIII to XVIII. 



Directions. Apply the tests to each substance separately 

 and tabulate your results as follows: 



