I50 STEMS 



Plants with prostrate stems are especially abundant on 

 sterile soil. You may have noticed them on sandy beaches 

 where plants with erect stems are very few and far between. 

 In such places prostrate plants have certain advantages. 

 There is the advantage that they are not in danger of 

 being shaded by other plants ; there is the advantage over 

 plants with erect stems that they are not so much exposed 

 to the danger of loss of water by evaporation more rapidly 

 than the roots can supply it; there is the advantage that 

 they are not called upon to devote nearly so much work 

 and material to the making of their stems as are erect 

 plants. Prostrate stems have another advantage over 

 erect stems in their chance to reproduce at every node. 

 So, all in all, there is a good deal to be said in favor of 

 prostrate stems, in spite of the fact that they are poor de- 

 vices for getting leaves up into the Light. 



Some plants with erect stems also produce prostrate 

 stems which appear to be for the express purpose of re- 

 production. You recall this in the case of the strawberry 

 plant whose prostrate stems or runners have been de- 

 scribed. (See Figure 40.) The common white clover also 

 reproduces by runners ; this matter is also illustrated in the 

 process of layering. (See Section 41.) Since all the nodes 

 of prostrate stems are in contact with the soil, there is the 

 chance for them to develop root branches as well as stem 

 branches and so establish new plants. 



Prostrate stems send up leaves from their upper side 

 only. Frequently you find prostrate stems twisted be- 

 tween one node and the next, so that side of the stem 

 which was under at one node is above at the next node. 

 Thus, though the leaves all arise from the side which is 

 upper at their point of origin, yet those at one node, on 



