SOIL AND ITS RELATION TO ROOTS 



77 



by this process of osmosis is sufficient to send water up the stem 

 to a distance, in some plants, of 25 to 30 feet. Cases are on 

 record of water having been raised in the birch a distance of 85 

 feet. 



Physiological Importance of Osmosis. — It is not an exaggera- 

 tion to say that osmosis is a process not only of great importance 

 to a plant, but to an animal as well. Foods are digested in the 

 food tube of an animal ; that is, they are changed into a soluble 

 form so that they may pass through the walls of the food tube and 

 become part of the blood. The inner lining of part of the food 

 tube is thrown into millions of little fingerlike projections which 

 look somewhat, in size at least, like root hairs. These fingerlike 

 processes are (unlike a root hair) made up of many cells. But 

 they serve the same purpose as the root hairs, for they absorb 

 liquid food into the blood. This process of absorption is largely 

 by osmosis. Without the process of osmosis we should be unable 

 to use much of the food we eat. 



Composition of Soil. — If we examine a mass of ordinary loam 

 carefully, we find that it is composed of numerous particles of vary- 

 ing size and weight. Between these particles, if the soil is not caked 

 and hard packed, we can find tiny spaces. In well-tilled soil these 

 spaces are constantly be- 

 ing formed and enlarged. 

 They allow air and water 

 to penetrate the soil. If 

 we examine soil under the 

 microscope, we find con- 

 siderable water clinging to 

 the soil particles and form- 

 ing a delicate film around 

 each particle. In this 

 manner most of the water 

 is held in the soil. 



How Water is held in 

 Soil. — To understand what comes in with the soil water, it will 

 be necessary to find out a little more about soil. Scientists who 

 have made the subject of the composition of the earth a study, 



Inorganic soil is being formed by weathering. 



