126 GENERAL BOTANY 



The roots which arise from the under side of creep- 

 ing plants like LIPPIA, and those by which, as we 

 have already learnt in chapter x, some climbers as like 

 PHILODENDRON and PIPER, cling to their supports, are 

 also adventitious. In the latter the geotropic tendency 

 is altogether absent while the apheliotropic is very 

 strong, so that they arise only on the darkened side 

 of the climbing stem, and make their way into the 

 cracks of the bark of the supporting tree. The 

 hanging roots of the Banyan, on the other hand, are 

 so much more sensitive to gravity than to light, 

 that they grow straight downwards, and can only 

 very occasionally be seen curving towards the main 

 trunk i.e. to the shadier side. 



Adventitious roots will arise on almost any piece of 

 a shoot axis, that is buried in the ground, or even 

 merely darkened, and on this account many plants can 

 be easily propagated. If pieces of the common Sugar- 

 cane or Prickly-pear, for instance, be stuck into or 

 even laid flat on the ground, roots soon grow out from 

 the nodes (where the spines are) and make their \vay 

 into the soil. The ordinary way of propagating the 

 common potato, sweet potato, hariyali-grass, and many 

 other plants depends on this property. In the case of 

 the common potato, a tuber (which we have learnt is 

 part of the shoot) or any part of it that contains an 

 * eye ' (or bud), may be used. In the case of the 

 Sweet potato, the tuber is part of the root- system, 

 but from any portion of the stem, as long as it contains 

 a node, roots and buds will grow out. 



Gardeners make use of this same habit of roots 

 growing out of buried or darkened portions of a shoot 



