Roots. 



33 



ing portions of the root, are continually brought into new 

 parts of the soil, where fresh supplies of materials, suit- 

 able for forming the food of the plant, are to be obtained. 



19. Importance of Root Hairs. The root hairs are organs 

 of much importance, since they greatly increase the anchor- 

 ing strength of the root and furnish 



an increased surface for the absorp- 

 tion of water and other substances 

 from the soil. (See photomicro- 

 graph of root and root hairs of bar- 

 ley, Fig. 11.) It has been estimated 

 that the hairs on corn roots, for in- 

 stance, increase the absorbing sur- 

 face about twelve times. When 

 plants are transplanted during the 

 growing season, after the leaves 

 have been formed, they are quite 

 certain to wilt, because the newer 

 rootlets with their root hairs are 

 broken off, even when the greatest 

 care is exercised. The best time 

 to transplant is, therefore, in the 

 fall, after the leaves have dropped off, or in the spring, 

 before the new growth begins. 



20. The Nature of the Soil. The value of a wide dis- 

 tribution of the roots in the soil lies in the fact that, aside 

 from the benefits of anchorage, plants must take from the 

 soil, w r ater and certain other substances without which they 

 could not live. The soil is therefore a subject of great 

 interest in connection with the study of plants. There are 

 various kinds of soils, but it may be stated in general that 

 ordinary tillable soil consists of particles of rocks in va- 

 rious degrees of disintegration, intermixed with vegetable 



FIG. ii. 



Photomicrograph of a root of 

 Barley, showing root hairs 

 forming near the apex and 

 dying away behind. X 3. 



