28 ELEMENTS OF BOTANY. 
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 ° 
roots which are adapted to live in water only. These water 
roots often show very large and distinct root-caps, as they 
do to a remarkable extent in the water-hyacinth already men- 
tioned. This plant is espe- 
cially interesting for labora- 
tory cultivation from the fact 
that it may readily be trans- 
ferred to moderately damp soil 
and that the whole plant pre- 
sents curious modifications 
when made to grow in earth 
instead of water. 
q 
4 42, Parasitic Roots.\— The 
(es dodder, the mistletoe, and a 
im good many other parasites 
8 ee live upon nourishment which 
they steal from other plants. 
The parasitic roots or hau- 
storia form the most intimate 
connections with the interior 
portions of the stem or the root, as the case may be, on which 
the parasite fastens itself. 
In the dodder, as is shown in Fig. 15, it is most interesting 
to notice how admirably the seedling parasite is adapted to 
the conditions under which it is to live. Rooted at first in 
the ground, it develops a slender, leafless stem, which, lean- 
ing this way and that, no sooner comes into permanent 
contact with a congenial host (as the supporting plant is 
called) than it produces haustoria at many points, gives up 
further growth in its soil roots, and grows rapidly on the 
Fic. 14, — Aerial Adventitious Roots of 
the Ivy. 
1 See Kerner and Oliver’s Natural History of Plants, vol. I, pp. 171-213. 
