FOODS 53 



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 one of the most 

 important problems 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. 



What are Foods? — We have some knowledge of foods in our 

 daily life. We eat meat, vegetables, fruits, and cereals ; we know 

 that they have come from the bodies of plants or animals. That 

 such foods are organic (of living origin) there can be no doubt. 

 But we could not live without water, which is inorganic (of non- 

 living origin) ; and experiments have proved that both plants 

 and animals need certain compounds of iron, potassium, sodium, 

 and other mineral salts, in order to live. It is evident, then, that 

 foods may be organic or inorganic. 



Organic Nutrients. — Organic foods are made up of two kinds of 

 substances, the nu'trients and the wastes or refuse. The organic 

 nutrients are classed in four groups : 



Carhohy'drates are the simplest of the very complex chemical 

 compounds called organic nutrients. They are composed of car- 

 bon, hydrogen, and oxygen, the two latter elements in a propor- 

 tion to form water. Starch (CeHioOs) and grape sugar (C6H12O6) 

 are common examples of carbohydrates. 



Fats and Oils are, like carbohydrates, composed of carbon, 

 hydrogen, and oxygen, but in some proportion which enables 

 them to unite readily with oxygen. 



Proteins (pro'te-inz) are the most complex of all nutrients in 

 their composition, and have, besides carbon, oxygen, and hydro- 

 gen, the element nitrogen and minute quantities of other 

 elements. 



Vitamins (vi'td-mmz), a very important group which will be 

 discussed in a later chapter. 



Test for Starch. — If we boil water with some laundry starch 

 m a test tube, then cool it and add to the mixture two or three 



B. NEW CIV. BIOL. — 5 



