THE ROOT— FUNCTION AND STRUCTURE 



41 



"baked" (Fig. 43) contain very little moisture or air, — 

 not so much as similar soils that are granular or mellow. 



Proper Temperature for Root Action. — The root must be 

 warm, in order to perform its functions. Should the soil of 

 fields or greenhouses be much colder than the air, the 

 plant suffers. When in a warm atmosphere, or in a dry 

 atmosphere, plants need to absorb much water from the 

 soil, and the roots must be warm if the root-hairs are to 

 supply the water as rapidly as it is needed. If the roots are 

 chilled, the plant may wilt or die. 



Roots need Air. — Corn on land that has been flooded by 

 heavy rains loses its green color and turns yellow. Besides 

 diluting plant-food, the water drives the air from the soil, and 

 this suffocation of the roots is very soon ap- 

 parent in the general ill health of the plant. 

 Stirring or tilling, the soil aerates it. Water 

 plants and bog plants have adapted them- 

 selves to their particular conditions. They 

 get their air either by special surface roots, 

 or from the water through stems and leaves. 



Rootlets. — Roots divide into the thijinest 

 and finest fibrils : there ai'e roots and there 

 are rootlets. The smallest rootlets are so 

 slender and delicate that they break off 

 even when the plant is very carefully lifted 

 from the soil. 



The rootlets, or fine divisions, are clothed with the root- 

 hairs (Figs. 44, 45, 46). These root-hairs attach to the 

 soil particles, and a great amount of soil is thus brought 

 into actual contact with the plant. These are very deli- 

 cate prolonged surface cells of the roots. They are borne 

 for a short distance just back of the tip of the root. 



Rootlet and root-hair differ. The rootlet is a compact 



Fig. 44. — Root- 

 hairs OF THE 

 Radish. 



