262 NATURE STUDY AND AGRICULTURE 



proteid as you did the egg. You may have to wait several 

 hours before you can be sure of a change of color. A good 

 plan is to start a number of tests on a plate and set away 

 till the next day. Test different parts of the corn grain, 

 squash seed, etc. What part of the corn grain shows the 

 most proteid ? What part the least ? 



There is another substance in plants for which you do 

 not need to make a chemical test. You have been testing 

 it all your life. Why does a sweet potato taste sweeter 

 than the common white potato? Name other plants that 

 have sugar in them. From what plants is the sugar of 

 commerce obtained ? All starch found in plants is changed 

 into sugar before it can be absorbed by plants or animals, 

 for starch is insoluble, and all substances absorbed by 

 living bodies must be dissolved. 



Is there any part of your corn grain that does not seem 

 to have any of these substances named above ? The hulls 

 are made up mostly of a substance called cellulose. Cellu- 

 lose is found in all plants, and is the material that gives 

 strength and firmness to the different parts. It is found 

 in the cell walls, in fibers of stems, roots, and leaves, as well 

 as in fruits and seeds. It is harder and thicker in some 

 parts of plants than others, as in stems, husks, and roots. 

 The fibers of cotton, hemp, and flax are made chiefly of 

 cellulose. Soak some common newspaper or writing paper 

 in water till all the sizing is washed out. The pulp which 

 remains is almost pure cellulose. 



Cellulose may be obtained from plants by the following 

 process : Dry thoroughly some stalks of corn or sunflower. 

 Pulverize as fine as possible. Cover with water in which 

 are a few drops of sulphuric or hydrochloric acid, and boil 



