USES OF ROOTS. 31 



seed. In many plants, however, roots arise 

 not only in this manner but also from stems. 

 A good example is the common pumpkin, 

 which puts down thick, white roots as it trails 

 over the ground. It is obvious that these roots 

 carry on the ordinary work of absorption of 

 water, because if the main root dies or is cut 

 away the plant is unaffected. 



4. In some plants the roots formed above 

 ground are also of use as supports, thus in 

 maize and Guinea corn a number of roots arise 

 from the stem, at some distance above the soil, 

 grow downwards and anchor the plant firmly. 

 In the mangrove and screw-pine such roots are 

 still more obvious and form the curious, stilt- 

 like supporting structures. Stem -borne roots 

 may, moreover, be of assistance to a plant 

 in climbing upon walls, trees, etc. as may be 

 seen in the vanilla and the wax-plant (Hoya). 



5. In the case of many plants, a portion 

 of the stem, separated from the parent plant, 

 so that it no longer receives supplies of water 

 and food, shows a tendency to attempt to save 

 its life by producing roots of its own. In this 

 effort it will usually be successful if it happens 

 to be placed in a moist spot. Full advantage 

 is taken of this tendency by gardeners and 

 agriculturists ; indeed, we can have no better 



