12 HOW PLANTS GROW 



Put a little water 'in a test-tube and add a pinch of cornstarch. Add a few 

 drops of iodine solution (a 10 per cent solution is strong enough). 



Shave down a corn grain from the germ side and test for starch by 

 applying iodine with a brush. Do all parts show starch? 



Test other cereals for starch; also peas, beans, and slices of potato, 

 turnip, beet, and carrot. 



Protein is identified by nitric acid, giving a bright yellow reaction. 

 Test the same materials as above for protein. 



Soak a few wheat grains until soft and make very thin slices with a 

 sharp razor. Mount some in iodine solution (five per cent) and others in 

 weak nitric acid. Examine under microscope for structure of cells and 

 location of starch grains and protein. 



Mount a bit of flour in each solution and examine. Is flour pure 

 starch ? 



Loss of Water by Plants. Grow a sunflower or castor bean plant in 

 a six-inch pot. When six to ten inches high, prepare for the experiment as 

 follows : 



Water the plant well. Then cover the pot and soil with a rubber cloth 

 or melted paraffine. This will prevent all water escaping except through the 

 plant leaves. Now weigh the pot, and continue to weigh daily while plant 

 lives. 



Observe the daily water loss. Does it vary from day to day? 



If a second plant be prepared in a similar way, and covered with an in- 

 verted glass jar, the water lost by the plant will be collected. 



Moisture in Corn. When, corn is kept under different conditions its 

 moisture content will vary considerably. Take samples that have just been 

 liusked, or husked corn remaining in the open, or corn from cribs, or corn 

 from a dry seed room. (Compare these samples as follows: Grind finely a 

 few ounces of each sample in a coffee mill. Weigh one ounce or one gram 

 of each. Then dry the weighed lots in an oven without burning, and reweigh 

 each. Determine the percentage of moisture by dividing the loss in weight 

 of each sample by its dry weight. Moisture in other grains may be de- 

 termined in the same way (Chapter XXIV). 



QUESTIONS 



1. Name the principal parts of a plant and tell briefly the functions of each. 



2. What do you understand by " element "? 



3. How many elements in a plant ? 



4. Where does a plant get them ? 



5. How can a plant get elements from the soil? 



6. How do plants get carbon? 



7. Have you ever seen carbon? 



8. What is " dry matter "? 



9. How much dry matter in a l&le ( 100 pounds) of hay? 



10. If you burn the bale of hay, about how much ash will remain? 



11. Where did the ash come from? 



12. Where did the rest of the " dry matter " come from? 



13. How long are plant roots? 



14. What are root-hairs and what do they do? 



15. Can you explain osmosis? 



16. Why must plants take up so much water from the soil? 



17. How does the water escape? 



18. What do leaves do? 



19. What is the " plant food " made by leaves? 



20. How does it get to other parts of the plant? 



21. How does protein differ from carbohydrates? 



