THE SOIL AND THE PLANT 113 



When the soil can be easily pulverized, and contains 

 plenty of organic matter, it is said to be in good tilth. 

 This condition is favorable for root growth. It enables 

 the roots to extend themselves more readily between 

 and around the loose particles, and it makes easy the 



SOIL IN GOOD TILTH. 



work of the delicate root hairs through which the plant 

 absorbs its food. 



Plants require not only that the soil be in good tilth, 

 but also that it contain such plant foods as they need and 

 that it have these foods in such a state as to be usable. 

 Soil water holds some carbon dioxide (a gas), which comes 

 from the air, and various mineral substances in solution 

 as water in a cup may hold salt or sugar in solution. 

 Plants absorb soil water through their roots. Most of it 

 they give off again through their leaves but first they take 

 from it such of the minerals as they can use for food. A 

 fertile soil must have a sufficient supply of soil water and 

 the necessary mineral substances for this water to take up 

 to feed plants. We will now see what these plant foods are. 



