STEUCTUEE AND WOEK OF PLANTS 



17 



Sugar and starch may be used as food by the plant, being 

 transported to and made into the living parts of the plant. 

 Or these things may be made 

 into more complex foods, (LrH4- 

 known as the proteins, by uif 

 the addition of some of the 

 compounds of nitrogen, potassium, 

 phosphorus, or other substances, 

 and then digested and used by the 

 plant. Replenishment and growth 

 of new parts can take place only 

 by means of foods, and since the 

 plant makes its own supply, the 

 importance of the process is very 

 great. 



Manufactured foods are carried 

 to all the living parts of the plant. 

 They may also be stored in almost 

 any plant structure. When in proc- 

 ess of moving through the plant, 

 these foods are believed to pass 

 through the soft portions of the 

 fibrovascular bundles. 



Furthermore, often more food is 

 made by green plants than they 

 need at the time, or even, in case 

 of some plants, than they ever use, 

 and this is stored most commonly 

 in the form of starch, though some- 

 times in other forms. This stored 

 food may be used later by the 

 plant, or as food for men and other 

 animals. It may also be moved by 

 the plant and stored in a different 

 structure from that in which it was 

 first located. 



. 12. Apparatus for collect- 

 ing oxygen from working plants 



Water plants are submerged with 

 one end in the mouth of the grad- 

 uate. Bubbles of oxygen pass 

 upward from the cut ends of the 

 stems and crowd out some water 

 from the previously filled grad- 

 uate. The ordinary test for oxy- 

 gen with a burning stick will 

 determine whether it is present. 

 In such an experiment care must 

 be taken to see that there is 

 plenty of space about the collect- 

 ing tube to permit free passage 

 of the gases that are in the water. 

 After Ganong 



