SOIL AND ITS RELATION TO ROOTS 73 



Experiments to determine the Influence of Moisture on a Grow- 

 'ing Root. — The objection might well be interposed that possibly 

 the roots in the pocket garden ^ grew downward after water. That 

 moisture has an influence on the growing root is easily proved. 



Plant bird seed, mustard or radish seed in the underside of a 

 sponge, which should be kept wet, and may be suspended by a 

 string under a bell jar in the schoolroom window. Note whether 

 the roots leave the sponge to grow downward, or if the moisture 

 in the sponge is sufficient to 'counterbalance the force of gravity. 



Water a Factor which determines the Course taken by Roots. — 

 Water, as well as the force of gravity, has much to do with the direction 

 taken by roots. Water is always found below the surface of the 

 ground, but sometimes at a great depth. Most trees, and all 

 grasses, have a greater area of surface exposed by the roots than 

 by the branches. The roots of alfalfa, a cloverlike plant used for 

 hay in the Western states, often penetrate the soil after water for 

 a distance of ten to twenty feet below the surface of the ground. 



Fine Structure of a Root.- — When we examine a delicate root 

 in thin longitudinal section under the compound microscope, 

 we find the entire root to be made up of cells, the walls of which 

 are uniformly rather thin. Over the lower end of the root is 

 found a collection of cells, most of which are dead, loosely arranged 

 so as to form a cap over the growing tip. This is evidently an 

 adaptation which protects the young and actively growing cells 

 just under the root cap. In the body of the root a central cylinder 

 can easily be distinguished from the surrounding cells. In a 

 longitudinal section a series of tubelike structures may be found 

 within the central cylinder. These structures are cells which have 

 grown together at the small end, the long axis of the cells running 



1 The Pocket Garden. — A very convenient form of pocket germinator may be 

 made as follows. Obtain two cleaned four by five negatives (window glass will 

 do) ; place one flat on the table and place on this half a dozen pieces of colored 

 blotting paper cut to a size a little less than the glass. Now cnt four thin strips of 

 wood to fit on the glass just outside of the paper. Next moisten th(^ blotter, place 

 on it some well-soaked radish, nmstard seeds or barley grains, and cover with the 

 other glass. The whole box thus made should be l)ound together with bicycle tape. 

 Seeds will germinate in this box and with care may live for two weeks or more. 



2 Sections of tradescantia roots are excellent for demonstration of these structures. 



