44 THE NATURE AND WOHK OF PLANTS 



seedling to a cork, as in § 43, using a very long 

 pin, but placing tlie root with tlie tip pointing 

 downward but not touching the water or the cork. 

 Now cut the smallest bit of paper you can handle, 

 and fasten to one side of the extreme tip by means 

 of gum arabic softened in water, or shellac. Observe 

 four or five hours, and a day later, and the apex 

 of the root will be seen to have curved away from 

 the side to which the paper was attached, exactly 

 as it would bend away from a hard object in its 

 path. Some difficulty may be experienced in attach- 

 ing the paper properly, and the experiment should 

 be repeated until some decisive result is at hand. 



49. The roots of air plants. — There are a large 

 number of species which inhabit the warmer coun- 

 tries that never reach the soil, but live upon the 

 branches of trees, to which they cling by means of 

 climbing roots, such as were mentioned in § 28. 

 They also form long cordlike roots which hang 

 downward sometimes twenty or even forty feet in 

 length, with the diameter of a lead pencil. In 

 some instances these reach the soil, and then 

 branches are formed. Generally, however, these 

 aerial roots are papery white in color and have a 



