SEEDS AND SEEDLINGS 67 



don which has been previously soaked in water, and test for starch 

 with iodine solution, the characteristic blue-black color appears, 

 showing the presence of the starch. If a little of the stained mate- 

 rial is mounted in water on a glass slide under the compound micro- 

 scope, 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. 



Starches and sugars make up the great class of nutrients known 

 as carbohydrates. Of these we shall learn more when we take up 

 the study of foods. (The teacher may here refer to the chapter 

 on Foods.) 



Proteid in the Bean. Another nutrient present in the bean 

 cotyledon is proteid. Several tests are used to detect the presence 

 of this nutrient. The following is one of the best known: 



Place in a test tube the substance to be tested ; for example, a 

 bit of hard-boiled egg. Pour over it a little strong (80 per cent) 

 nitric acid. Note the color that appears a lemon yellow. If 

 the egg is washed in water and a little ammonium hydrate added, 

 the color changes to a deep orange, showing that a proteid is 

 present. 



If the proteid is in a liquid state, its presence may be proved 

 by heating, for when it coagulates or thickens, as does the 

 white of an egg when boiled, proteid in the form of an albumin 

 is present. 



Another characteristic proteid test easily made at home is 

 burning the substance. If it burns with the odor of burning feathers 

 or leather, then proteid forms part of its composition. 



Proteids occur in several different forms, but the preceding tests 

 will cover most cases commonly met. White of egg, lean meat, 

 beans, and peas are examples of substances composed in a large 

 part of proteid. 



A test of the cotyledon of a bean for proteid food with nitric acid 

 and ammonium hydrate shows us that considerable proteid is 

 present. It contains not less than 23 per cent of proteid, 57 per 

 cent of carbohydrates, and about 2 per cent of fats. 



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. 



