50 THE PLANT: A GENERAL EXTERNAL VIEW 



Stems tend to grow up as roots tend to grow down. 

 Roots place the root-hairs in positions favorable to the 



absorption of water. Stems 

 place the leaves in positions 

 favorable to the absorption 

 of light. 



Stems are jointed. Roots 

 are not. In old stems the 

 joints are often hard to see. 

 They often disappear as the 

 stem enlarges. In young 

 stems, however, they are very 

 plain. These joints are called 

 nodes. The lengths of stem 

 between the nodes are called 

 internodes. Corn stems show 

 nodes and internodes very 

 plainly. It is at the nodes 

 that leaves and branches regu- 

 larly arise from stems. (See 

 Figure 5.) It is because they 

 possess nodes and internodes 

 that some underground struc- 

 tures, like the potato, are 

 known to be stems and not 

 roots. 



In the section on nutrition 



you learned that green plants 



make their own food. By 



green plants we mean those 



„ , , . ... plants which have some green 



Fig. S- — Phlox, snowing nodes and in- * ° 



temodes and a flower cluster. parts. Leaves, of course, are 



