CHAPTER XI 



THE WORK OF STEMS 



71. The Functions of Stems. — The three functions 

 which Nature has given stems to perform seem to be : 



First : to hold the leaves up to the Ught that they may 

 manufacture food. 



Second : to conduct the water and dissolved minerals 

 from the roots to the leaves. 



Third : to conduct the food manufactured in the leaves 

 back again to the roots and other parts of the plant. 



72. The Forms of Stems. — In the effort to hold their 

 leaves up to the Ught, stems grow in three fairly distinct 

 forms; (1) prostrate, or trailing, (2) climbing, and (3) 

 erect. 



73. Prostrate Stems. — Plants which form this kind of 

 stems are often overshadowed by those with erect stems. 

 Notwithstanding this fact, a large number of plants have 

 prostrate stems. Such plants as the prostrate pigweed, 

 purslane, sweet potato and the dooryard weed, or knot- 

 weed all have this form of stem. Because of their clinging 

 closely to the ground, these plants require less moisture 

 than they would if the stems were higher in the air. The 

 stems themselves act as a mulch to prevent the escape of 

 moisture from the soil while often at the joints roots are 

 formed. 



Even when these plants grow among the erect plants 

 as the purslane or crab grass grows among the com, the 



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