190 TEXTBOOK OF BOTANY 



such as the Hly, may form branches underground. The 

 common greenhouse palms .are familiar examples of plants 

 whose stems ordinarily bear no vegetative branches. But 

 their large flower clusters show that these stems, too, may 

 branch. Indeed, it would be difficult to name a plant whose 

 stem never branches under any circumstances ; and it is only 

 for the purpose of making a convenient distinction that the 

 stems of most palms and of many other monocotyledons are 

 said to be unbranched. On the other hand, the stems of most 

 dicotyledons and gymnosperms branch abundantly. In its 

 inner structure, and in the various forms that it may take, 

 a branch of any plant is usually like the main stem, although 

 there are certain special forms of branches that will be referred 

 to later. It is often convenient to use the word shoot, mean- 

 ing by it either a stem or a branch, together with the leaves 

 and such other structures as it may bear. 



211. Erect Stems. — The stems of a large proportion of 

 seed plants grow upright and, whether herbaceous or woody, 

 they form enough thick-walled tissue to support their own 

 weight and that of their branches, leaves, and flowers. The 

 great advantage to the plant of having an erect stem is that 

 its leaves are carried upward and are separated so as to 

 receive the greatest possible amount of light. We have 

 already seen why light is necessary to green plants ; and the 

 effect of a partial lack of light is seen in the scarcity of small 

 plants in a deeply shaded forest. An erect stem may be very 

 much branched, like that of a pine ; or, like that of a palm, it 

 may be unbranched except in connection with a special pur- 

 pose such as flower production. The shape of a plant wnXh. a 

 branching stem depends in part upon the comparative rate 

 of growth of the main stem and of the branches. In some 

 trees the main stem grows more rapidly, and consequently 

 is always longer, than any of its branches. If all the branches 

 of such a tree grow at about the same rate, the lowest, ones, 

 being the oldest, are also the longest, and each branch is 



