28 



ELEMENTS OE 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 modiiications 

 when made to grow in earth 

 instead of water. 



42. Parasitic Roots} — The 

 dodder, the mistletoe, and a 

 good many other parasites 

 live upon nourishment which 

 they steal from other plants. 

 The parasitic roots or haii- 

 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. Eooted 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 



> See Kerner and Oliver's Natural History of Plants, vol. I, pp. 171-213. 



Fig, 14. —Aerial Adventitious Eoots of 

 the Ivy. 



