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 

 whitisli 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 



