Ch. IV, 2] 



STRUCTURE OF STEMS 



115 



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

 Redwood is kno\\ii 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, huwever. mere age is in 

 C|uestion, there are proljably much older plants, fur the Sphag- 

 num mosses of peat l>ogs appear to have liad a continuous 

 grofl-th from the inception of the liogs at the close uf 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 fohage, as will later appear. It is easily 

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

 leaves, — for sterns usually grow from buds in the axils of 

 leaves, while leaves have buds in their axils. 



2. The Structvke of Stems and Support of the Foliage 



The primary function of stems, and their distinctive con- 

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

 spread of the foliage. Theremth. however, are involved 

 minor functions, notabh" _-,_ 



conduction of water and 

 food, with grov,-th, respira- 

 tion, and self-adjustment to 

 prevaiHng conchtions. 



T}-pical foHage-support- 

 ing stems are herbaceous 

 when young, Ijut commonly 

 become woody with age. 



Herbaceous stems, whetlier 

 true herbs or the herbaceous 

 tips of woody branches, are 

 tj-pically cylindrical and 

 upright, and produce the 

 leaves horizontally all 



arouni 



d. At the tip is a Kemer.) 



Fig. 69. — A topical leaf-bearing 

 stem, of Norway Maple ; X j. iFrom 



