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. — Man A 
nN 
plants, such as the willow, 
readily adapt their roots to 
live either in earth or in water, ~ 
and some, like the little float- Fie. 13.— Aerial 
ing duckweed, regularly pro- °° "Ores 
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 
1Specimens of the lower part of the cornstalk, with ordinary roots and 
aerial roots, should be dried and kept for class study. 
