56 PLANT GROWTH AND NUTRITION 



step by step, the general concepts of the necessity for food, for digestion of food, 

 and for the oxidation of food for the release of energy. The food tests are inci- 

 dentally shown, as they should be, in connection with the main problem of food in 

 its relation to the young plant. All tests as tests are subordinated to the main 

 problems as outlined above. Thus the pupil gets his incidental information about 

 certain factors of the environment of the young plant by means of association. 

 Throughout this entire chapter a conscious effort should be made by the teacher 

 to correlate the processes which go on in the young developing plant with the same 

 fundamental processes wdiich go on in the human body. Thus experimental proof 

 lays a foundation for the work in human physiology later. 



Problem 25 : To find the relation of the embryo to the food 

 supply. 



Materials. — Dry pods containing beans, soaked beans. 



Method and Observations. — Open the pods and pull a bean 

 from its attachment. Note the scar where the bean was attached. 

 This is called the kilum. 



Look for a tiny hole, the micropyle, at one end of the hilmn. 

 It was through this hole that the sperm cell reached the egg cell 

 {micropyle means ''little gate"). 



Peel off the outer coat (testa) of a soaked bean. What use 

 might it have ? 



Note that the bean separates into two parts, called the cotyledons. 

 Take off one cotyledon very carefully, and find two tiny folded 

 leaves, the plumules, and a rodlike part, the hypocotyl. How does 

 the hypocotyl point with reference to the hilum edge of the bean? 



All the parts within the seed coat are collectively known as 

 the embryo. 



Conclusion. — 1. How is the embryo protected? 



2. Can you find a use to the young plant of the hypocotyl? 

 The plumule? The cotyledon? 



3. Compare the bean seed with some growing beans (seedlings) 

 a week or two old. How can you answer the questions above? 



4. Notice in the older beans the cotyledons seem to be smaller 

 than in the beans that have not sprouted. To account for this 

 let us learn how to test for certain food substances or nutrients, 

 then after making these tests, apply the same tests to the bean 

 cotyledon and draw some valid conclusions as to the use of the 

 cotyledon. 



