STEMS 



47 



multiplication of plants in others. In many plants, as the 

 prostrate stem advances over the ground, roots develop from 

 the nodes and enter the soil, leaves are formed, and a new 

 plant is started, which may become independent by the 

 death of the older parts. In this way a plant may spread 

 over the ground, multiplying itself indefinitely. So 

 effective is this method of multiplication that plants with 

 erect stems often make use of it, sending out from near the 

 base special prostrate branches which advance over the 

 ground and start new plants. A very 

 familiar illustration is furnished by the 

 strawberry-plant, which sends out peculiar 

 leafless runners to strike root at the tip and 

 start new plants, which become independent 

 by the death of the runners (Fig. 46). 



These various prostrate stems illustrate 

 the fact that nodes can produce not only 

 leaves and branches, but also roots, if 

 placed in suitable conditions. Advantage 

 is taken of this fact in the common process 

 of layering, in which such stems as those 

 of blackberries and raspberries are bent 

 down to the ground and covered with soil, 

 when the nodes strike root and new plants 

 are started. 



(3) Climbing stems. A great many 

 plants have developed the ability to sus- 

 tain themselves by using supports. Al- 

 though not able to stand alone, by using 

 these supports they may attain great length 

 and display their leaves to light even in a 

 dense forest. This climbing is effected in 

 a variety of ways. In some cases, as the morning-glory, 

 bean, and hop-vine, the stem twines about the support, 

 such plants often being distinguished as twiners (Fig. 47); 



bean 



twining about 

 support. 



