SEEDS AND SEEDLINGS 67 



true leaves folded together between the cotyledons. How many leaves 

 are there ? That part of the plant above the cotyledons is known as the 

 -plumule or epicotyl (meaning above the cotyledons) . Later we shall wish to 

 know what part of the future plant the epicotyl forms. 



All the parts of the seed within the seed coats together form the embryo 

 or young plant. 



Draw the bean to show all the above parts, twice natural size. Label 

 every part carefully. 



Food in the Cotyledons. — The problem now before us is to find 

 out how the embryo of the bean is adapted to grow into an adult 

 plant. Up to this stage of its existence it has had the advantage 

 of food and protection from the parent plant. Now it must begin 

 the battle of life alone. We shall find in all our work with plants 

 and animals that the problem of food supply is always the most 

 important problem to be solved by the growing organism. Let 

 us see if the embryo is able to get a start in life (which many 

 animals get in the egg) from food provided for it within its own 

 body. 



Experiment. — Mash up a little piece of a bean cotyledon which you 

 have previously soaked in water. Test for starch with iodine solution 

 What color appears? If you now mount a little of 

 the stained material in water on a glass slide under 

 the compound microscope, you will find that the 

 starch is contained in the form of little ovoid bodies 

 called starch grains. The starch grains and other 

 food products are made use of by the growing plant 

 in a manner which we shall later know more about. 



Test the cotyledon of a bean, for proteid food, 

 with nitric acid and ammonium hydrate. The change 

 of the color of the surface shows us that considerable 

 proteid is present. According to the compilations 

 from the government reports, the kidney bean is one 

 of the materials very rich in proteid food. It con- Starch grains in the cells 

 tains not less than 23 per cent of proteid, 57 per cent of a potato tuber, 



of carbohydrates, and about 2 per cent of fats. 



Test a bean by heating it on a piece of paper in the oven to see if the 

 small quantity of oil present can be detected by this means. 



The above tests show us that the bean seed contains a large 



supply of food which, as we shall see, is used by the young plant 



in its germination. 



Germination of the Bean, Pea, and Com. — Soak the seeds at least eight 

 hours in water before planting. In general, the larger the seed the longer 

 the immersion in water before planting. For use in the laboratory seeds 

 may be planted in shallow boxes or trays. Use sawdust, clean white 

 sand, or sphagnum moss to plant them in. Make holes in the bottom of the 

 boxes for drainage. Plant beans about half an inch deep; smaUer seeds 



