CH. IV, 2] 



STRUCTURE OF STEMS 



115 



conditions can attain to a great size and age. Thus the giant 

 Redwood is known to exceed two thousand years in age, some 

 trees now standing being probably older than the Christian 

 era, while the Dragon Tree of the Canary Islands has been 

 claimed to live even longer. If, however, mere age is in 

 question, there are probably much older plants, for the Sphag- 

 num mosses of peat bogs appear to have had a continuous 

 growth from the inception of the bogs at the close of the 

 glacial period, many thousands of years ago. 



Stems, like leaves, perform also special functions, when 

 suitably modified in structure, forming tendrils, storage 

 organs, and even foliage, as will later appear. It is easily 

 possible, for the most part, to distinguish such stems from 

 leaves, for stems usually grow from buds in the axils of 

 leaves, while leaves have buds in their axils. 



2. THE STRUCTURE OF STEMS AND SUPPORT OF THE FOLIAGE 



The primary function of stems, and their distinctive con- 

 tribution to the plant's mode of life, is the support and 

 spread of the foliage. Therewith, however, are involved 

 minor functions, notably 

 conduction of water and 

 food, with growth, respira- 

 tion, and self -adjustment to 

 prevailing conditions. 



Typical foliage-support- 

 ing stems are herbaceous 

 when young, but commonly 

 become woody with age. 



Herbaceous stems, whether 

 true herbs or the herbaceous 

 tips of woody branches, are 

 typically cylindrical and 

 upright, and produce the 



, , . FIG. 69. A typical leaf-bearing 



leaves horizontally ^ all st em, of Norway Maple ; X i (From 



around. At the tip is a Kemer.) 



