86 



ROOTS AND THEIR WORK 



Another experiment is the following : Divide the interior of a shallow 

 wooden b.ox into two parts l\v an incomplete partition. Partly fill the box 

 with sawdust and place the opening in the partition so that it is below the 

 surface of the sawdust. Plant peas and beans in the sawdust on one side 

 of the partition, water very shghtly, but keep the other side of the box 

 well soaked. After two weeks, take up some of the seedlings and note the 

 effect on the roots. 



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 sur- 

 face of the ground, but 

 sometimes at a great depth. 

 In order to obtain a supply 

 of water, the roots of plants 

 frequently spread out for 

 very great distances. Most 

 trees, and all grasses, have 

 a greater area of surface 

 exposed by the roots than 

 by the branches. The mes- 

 quite bush, a low-growing 

 tree of the American and 

 Mexican deserts, often sends 

 roots downwards for a dis- 

 tance of forty feet after 

 v>-ater. 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. 



Structure of a Taproot. — To understand fully the structure of 

 the root, it will be necessary for us to examine some large, fleshy 

 root (a taproot), so that we may get a little first-hand evidence as 

 to its internal structure. If you cut open a parsnip or carrot so as 

 to make a cross section of the root, you find two distinct areas — an 

 outer portion, the cortex, and an inner part, the wood. If you cut 

 another parsnip in lengthwise section, these structures show still 



Dandelion plant. Note the length of the root. 

 Photographed by Overton. 



