80 A TEXT-BOOK OF BOTANY 
41. Special forms of roots.—Roots in the soil serve the 
double purpose of anchoring the plant and absorbing wa- 
ter, but certain roots hold other relations and need special 
mention. 
(1) Prop roots.—In certain plants roots are sent out 
from the stem or the branches, and finally reaching the 
ground establish the usual soil relations. Since these roots 
resemble braces or props, the name prop roots has been ap- 
plied to them (Fig. 77). A very common illustration is 
that of the corn-stalk, which sends out such roots from the 
lower nodes of the stem. More striking illustrations, how- 
ever, are furnished by the banyan and the mangrove. The 
banyan sends down from its wide-spreading branches prop 
roots, which are sometimes very numerous. When they 
enter the soil they often grow into large trunk-like sup- 
ports, enabling the branches to extend over an extraordi- 
nary area. There is record of a banyan cultivated in 
Ceylon with 350 large and 3,000 small prop roots, and 
able to cover a village of one hundred huts. The man- 
grove is found along tropical and subtropical seacoasts, 
and gradually advances into the shallow water by drop- 
ping prop roots from its branches and entangling the 
detritus (Fig. 307). 
(2) Water roots—If a stem is floating, clusters of 
whitish thread-like rootlets usually put out from it and 
dangle in the water. Plants which ordinarily develop soil 
roots, if brought into proper water relations, may develop 
water roots. For instance, willows or other stream-bank 
plants may be so close to the water that some of the root 
system enters it. In such cases the numerous clustered 
roots show their water character. Sometimes root systems 
developing in the soil may enter tile drains, when water 
roots will develop in such clusters as to choke the drains. 
The same bunching of water roots may be noticed when a 
hyacinth bulb is grown in a vessel of water, It is evident 
