96 SOILS AND PLANT LIFE 



Conclusion. — Determine how many grams per square 

 inch the plant has given off during the week. Reduce it 

 to ounces, considering that twenty-eight and three tenths 

 grams are equal to one ounce. 



How many tons of water will the velvet weeds in a 

 ten-acre field remove in one hundred days if each weed 

 throws off as much water per square inch of leaf surface 

 per day as the plant with which you have worked ? The 

 average leaf surface on each weed is two hundred square 

 inches and the average nmnber of weeds is two on each 

 square rod. 



70. Storage of Food in the Leaves. — The food which 

 is manufactured in the leaves is used by the plant in three 

 ways: 



First: to supply the plant with energy with which to 

 carry on the processes of growth. 



Second : to build the tissues of which its body is com- 

 posed. 



Third : It may be stored away for time of need, such as 

 drouth, dormant season, or to nourish the seedling after 

 germination. 



We have already seen how roots may be used as store- 

 houses of food. Leaves, like those of the cabbage, or 

 those which make up such bulbs as the onion, become 

 filled with reserve food, and for this reason are useful to 

 man. 



QUESTIONS 



1. Give three functions of leaves. 



2. Draw from memory a leaf considered as a mill, showing 

 how food is manufactured within it. 



3. Tell briefly and clearly how you proved that a leaf 

 manufactures starch, and that sunlight is necessary. 



4. Why win plants always reach for the light ? 



5. Name two reasons why starch is important. 



