ROOTS 37 



second of an inch long and is found just back of and inside 

 of the root cap, but merging into the second, where most 

 growth in length occurs. Fully grown cells may reach fifty 

 or more times their length at the time of cell division. When 

 fully developed they begin to change their character in the 

 region of the root hairs to become the various tissues of the 

 mature root. These areas of development may be located in 

 a general way on a young root similar to the one in Figure 

 10, when the root cap and dividing areas are slightly darker. 

 The root hairs appear as a white covering. 



Food storage is an important function of the roots of 

 biennials and perennials. The abundance of plant food 

 stored may be seen by covering a cross section of a root 

 with a solution of iodine^ for a few minutes, washing, and ob- 

 serving the blue-stained starch in the tissues of the root. 

 This is used during the rapid spring growth of root, stem, and 

 leaves. For this reason the plants which have favorable con- 

 ditions during the summer will have stored more food and 

 therefore will make a better growth the following spring. 

 Furthermore, most plants have rapid root growth before the 

 buds open in the spring, for which they depend entirely on 

 the stored food, therefore, it is likely that the successful grow- 

 ing of plants depends largely on the storage of food. Late 

 summer growth takes stored food which should be reserved 

 for spring and in addition the growth is so tender that it often 

 winter-kills. This can be largely regulated with fertilizers 

 as explained in Chapter 22. A perennial will usually have 

 more food stored in the root and the stem than will be used 

 for the spring growth, as may have been noted when a thrifty 

 plant has had enough reserve stored food to grow a new set 

 of leaves if the first set has been destroyed by frost or insects 

 in the early spring before storage had taken place. 



^ A solution of iodine for this purpose may be made by dissolving potassium iodide 

 in water at the rate of one-half ounce per quart of water and adding one-tenth of an 

 ounce of iodine crystals. 



