PROPER TEMPERATURE ROOTS EXCRETE 



71 



149. PROPER TEMPERATURE. — T/?e root must l)f 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 atmos- 

 phere, 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. Try this with two 

 potted plants, as radish, coleus, tomato, etc. Put one pot 

 in a dish of ice water, and the other in a dish of warm 

 water, and keep them in a warm room. 

 In a short time notice how stiff and 

 vigorous is the one whose roots are 

 warm, whereas the other may show 

 signs of wilting. 



150. ROOTS EXCRETE. — The plant 

 not only absorbs what is already solu 

 ble, but it is capable of rendering 

 soluble small quantities of the insoluble 

 substances present in the soil, and ivhich 

 may be needed for plant-food. The 

 plant accomplishes this result by 

 means of substances excreted by the 

 roots. These substances may even etch 

 marble. On a polished marble block, 

 place a half-inch of sawdust or soil, 

 in which plant seeds. After the plants 

 have attained a few leaves, turn the 

 mass of sawdust over and observe the 

 prints of the roots on the marble. 

 These prints will be very faint. An 

 illustration of this experiment is given on page 73. Care- 

 fully pull up a young seedling which is growing in soft 

 soil, and notice how tenaciously the soil particles are held 

 to the root (Fig. 110). 



110. The rootlets auil root- 

 hairs cling to the particles 

 of soil. 



