ROOTS 



37 



air-plants are grown in greenhouses. In such plants as the 

 ivy (Fig. 15) the aerial roots (which are also adventitious) 

 hold the plant to the wall or other surface up which it climbs. 

 In the Indian corn (Fig. 14) roots are sent out from 

 nodes at some dis- 

 tance above the 

 ground and finally 

 descend until they 

 enter the ground. 

 They serve both to 

 anchor the cornstalk 

 so as to enable it to 

 resist the wind and 

 to supply additional 

 water to the plant.^ 

 They often produce 

 no rootlets until they 

 reach the ground. 



50. Water-Roots. — Many 

 plants, such as the willow, 

 readily adapt their roots to 

 live either in earth or in water, 

 ■ and some, like the little floats 

 ing duckweed, regularly pro- 

 duce roots which are adapted to live in water 

 only. These water-roots often show large and 

 distinct sheaths on the ends of the roots, as, for instance, 

 in the so-called water-hyacinth. This plant is especially 

 interesting for laboratory cultivation from the fact that 



Fis. 13. — Aerial 

 Boots of ail Orchid.' 



I Specimens of tLe lower part of the cornstalk, with ordinary roots and 

 aerial roots, should be dried and kept for class study. 



