82 ELEMENTS OF BOTANY 
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 labora- 
tory cultivation from the fact that it may readily be 
transferred to moderately damp soil, and that the whole 
plant presents curious modifications when made to grow 
in earth instead of water. 
42. Parasitic Roots.1— The dodder, the mistletoe, and a 
good many other parasites live upon nourishment which 
they steal from other plants called hosts. The parasitic roots, 
or haustoria, form the most intimate connections with the 
interior portions of the stem or the root, as the case may be, 
of the host-plant on which the parasite fastens itself. 
In the dodder, as is shown in Fig. 14, it is most inter- 
esting 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, leaning this way and that, no sooner comes into 
permanent contact with a congenial host than it produces 
haustoria at many points, gives up further growth in its 
soil-roots, and grows rapidly on the strength of the sup- 
plies of ready-made sap which it obtains from the host. 
43. Forms of Roots. — The primary root is that which 
proceeds like a downward prolongation directly from the 
lower end of the hypocotyl. In many cases the mature root- 
system of the plant contains one main root much larger than 
any of its branches. This is called a taproot (Fig. 15). 
Such a root, if much thickened, would assume the form 
shown in the carrot, parsnip, beet, turnip, salsify, or radish, 
and is called a fleshy root. Some plants produce multiple 
1 See Kerner and Oliver’s Natural History of Plants, Vol. 1, pp. 171-213. 
