i8o 



General Botany 



Bureau of Science, P. I. 



Fig. io6. 



A mangrove swamp along the seashore of an island in the PhiUppines. The 

 prop roots support the plants in the soft mud. 



the poison ivy and trumpet creeper (Fig. iii) and act as hold- 

 fasts in supporting these climbers on trees and walls. Adventi- 

 tious roots may arise also at any point on a primary or secondary 

 root, following injuries. For example, when we plant pieces of 

 horse-radish or dandelion roots, adventitious roots develop. 

 During the dry season in deserts the younger parts of the root 

 system of some plants like the cactuses are dried out and killed, 

 and when the next wet season comes, many adventitious roots 

 develop from the parts of the root system still alive. In desert 

 plants these new adventitious roots do the absorbing work during 

 the moist period. 



In plants that propagate by " runners " and by underground 

 stems, all the roots that have developed from the horizontal 

 branches are adventitious. All plants that are commonly started 

 by bulbs, like the tulip, hyacinth, crocus, onion, and Hly, have 

 only adventitious roots. Probably all the plants of the potato, 

 sweet potato, yam, sugar cane, banana, dahlia, and peony that 



