274 FIRST YEAR COURSE IN GENERAL SCIENCE 



Another very important work of plants is the giving off 

 of oxygen from the carbon dioxide which the plant absorbs 

 from the air. The carbon only is used in starch making, 

 and the oxygen is passed out through pores in the leaves. 

 As starch making occurs naturally only in sunlight, so the 

 liberation of oxygen occurs only in the daytime. Oxygen is 

 not a waste product but a residue that is useless to the 

 plant. 



310. The Processes of Plant Nutrition. Plant nutri- 

 tion includes : 



The preparation of food from materials in soil, water, and 

 air. 



The digestion of these foods. 



The excretion of waste products of oxidation. 



The use of the foods in individual cells, either to make new 

 protoplasm in the process of growth and repair, or to yield 

 energy through oxidation by means of the oxygen taken from 

 the air. 



The elimination of any useless residue. 



EXERCISES 



1. Why do we not usually see the root hairs when a plant is 

 dug up? 



2. (a) Why does the gardener take pains to keep soil about the roots 

 of a plant which he is transplanting? (6) What is the effect on a plant 

 if the soil is dry? (c) Explain the change that watering produces. 



3. (a) In what state is the water given off from leaves of plants? 

 (6) Describe a simple method by which we could show that it is given 

 off. 



4. How can carbon dioxide reach the interior of a leaf? 

 6. What substances pass out of the pores of a leaf? 



6. What would be the appearance of a leaf after the chlorophyll 

 had been removed? 



7. Name some plants having simple leaves; others (besides the 

 bean) having compound leaves. 



8. What organs of a plant are its starch factories? 



9. How do the materials used there get to these organs? 



