PREVIEW 135 



seemingly be deprived of all plant food, yet live on fish which in 

 turn exist almost entirely on sea weeds and small microscopic plants. 

 Invariably we start with green plants which furnish food for animals. 



The green leaves of plants are really solar engines which get 

 power from the sun and which manufacture foods only when the 

 sun gives them this power. In order to make food the plant must 

 have certain raw material on which to work : carbon dioxide from 

 the air, and water and mineral salts from the soil. Another sub- 

 stance must be present in the leaves, a green coloring matter 

 called chlorophyll. This substance seems to be able to use the 

 radiant energy of the sun better than any other living material. 



But since the raw material, out of which foods are made, is in 

 the soil, the air, and the water which the plant receives, it is 

 evident that we must account for some way of getting these various 

 substances into the leaf. If one of the seedlings of a bean is 

 placed in sawdust and is given light, air, and distilled water, it 

 will die after the food in the cotyledons is used up. Soil is part 

 of its natural environment and the roots which come in contact 

 with the soil are very important structures. Not only does soil 

 hold water, but this water contains certain dissolved mineral 

 salts which are absolutely necessary for the life of the plant. 

 Distilled water does not contain these mineral salts which come 

 from the soil, consequently the plant will die. You have all read 

 of how plants can be kept alive by feeding them " plant pills." 

 These " plant pills " contain the necessary mineral salts which, 

 when dissolved in water, are absorbed through the roots into the 

 plant. These salts form a very important part of the living matter 

 of which both plants and animals are composed. Hence the 

 plant cannot grow without a small quantity of these materials. 



One of our big problems is to discover just how these dissolved 

 mineral substances are taken in by the roots. We say roots 

 absorb them, but how? A good scientist is not content with a 

 statement ; he wants proof. To obtain this proof he must use a 

 microscope and then he will see that the lower part of the small 

 roots are covered with tiny outgrowths from the living cells of 

 the root which immensely increase the absorbing surface of the 

 roots. These little projections, called root hairs, are the organs by 



