GERMINATION OF SEEDS 69 



Does the squash differ from the bean in the use of its 

 cotyledons to the plant (a) while germinating ? (6) later ? 



Does the difference in shape, thickness, and character 

 of the cotyledon in these seeds seem to have any relation 

 to its future use to the plant? 



Suggestion. Repeat the experiment, using castor beans 

 and any other available seed. 



54. THE FATE OF COTYLEDONS (optional) 

 Object. Same as in Experiment 52- 



Demonstration of the use of food by the young plant. 



1. With a razor or microtome prepare some very thin sec- 

 tions of cotyledons of bean, or pea, and mount them in a 

 drop of water under the microscope. Note the cells or com- 

 partments of which the cotyledon is built up. Note the 

 starch grains with which these cells are packed. 



Now place a drop of iodine solution at the edge of the 

 cover glass and watch the effect as it spreads over the starch 

 grains. 



2. Make a similar section of a cotyledon taken from a 

 seedling which has been growing for some time until the coty- 

 ledon has begun to show wrinkles. Mount it as before, 

 examine, and again treat it with the solution of iodine. How 

 do these cotyledons differ from the fresh ones (a) in plump- 

 ness, (6) in amount of starch in the cells? How can you 

 account for the difference ? What has become of the starch ? 



3. Make similar sections of the endosperm of corn and 

 castor beans, fresh and sprouted. Use iodine solution for 

 the corn. The oil in the castor bean needs no test to show 

 the difference. 



Suggestion. Germinate barley or any other cereal on 

 moist blotting paper. As soon as the first leaf begins to 



