THE ROOT. 31 



1. Pull up beans or peas that have been growing in saw- 



dust, and observe the entire root system. How 

 do the secondary roots compare with the primary 

 in their direction of -growth? If- roots of a higher 

 order have been formed, ascertain whether they 

 take the same direction as either of the preceding. 

 Would it be advantageous for the plant if all grew 

 downward ? 



2. Take a germinating pea or squash seed, with a radi- 



cle a centimeter or more in length, and fasten it 

 to a cork by a pin so that the radicle will point 

 horizontally. Keep it in a moist atmosphere under 

 a bell-jar, and exclude the light by covering with 

 a dark cloth. Observe the subsequent growth of 

 the radicle. Vary the experiment by turning 

 other specimens so that the radicle will point 

 nearly vertically. 



3. Tie a piece of netting over the mouth of a beaker or 



wide-mouthed bottle filled with water, and place on 

 it a number of seeds of white mustard that have 

 just begun to germinate. Allow the apparatus 

 to stand in front of a window without being dis- 

 turbed, filling with water occasionally, so that the 

 growth of the seedlings will be uninterrupted. 

 Observe the direction taken by the roots. 



VI. Examine different roots with reference to their 

 mechanical functions. 



1. The supporting roots of Indian corn. Notice where 



they originate, their direction of growth, and their 

 double action as braces and guys. 



2. Aerial roots of the English ivy, or trumpet-creeper. 



Compare these with ordinary roots. 



