ROOTS 31 
air-plants are grown in greenhouses. In such plants as the 
ivy (Fig. 18) the aérial roots (which are also adventitious) 
hold the plant to the wall or other surface up which it climbs. 
In the Indian corn roots are sent out from nodes at some 
distance above the ground and finally descend until they 
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Fic. 13. Aérial Adventitious Roots of the Ivy. 
enter the ground. They serve both to anchor the corn- 
stalk 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. 
41. 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 floating duckweed, regularly produce 
1 Specimens of the lower part of the“cornstalk, with ordinary roots and 
aérial roots, should be dried and kept for class study. 
