144 



STEMS 



internodes have deep parallel depressions and elevations; 

 winged when the cortex grows out as a narrow prominent 

 ridge as in broom tops; hairy when the surface is covered 

 with hairs. The surface of trees is smooth, rough or scaly. 



Fractures. Some stems are too fibrous to be fractured; 

 most stems, however, can be broken and their fracture is 

 similar to the fracture of roots. 



Outline of Sections. Sections are circular, triangular, 

 quadrangular, irregular or fluted in outline. 



FIG. 84. Strikingly colored bark of sycamore or buttonwood (Platanus 

 occidentalis), the light portions showing where the old bark has scaled off. 



Gross Internal Structure. The study of the stem would 

 not be complete without examining its cross section. In 

 most stems the cortex, wood and pith are clearly seen. In 

 herbaceous stems the pith makes up the greater part of the 

 stem, while in woody stems the pith is greatly reduced and 

 the wood makes up the bulk of the stem. In all cases observe 

 carefully the diameter, color and markings of the cortex, 

 wood and pith, and in addition observe whether the cambium 

 zone is distinct and carefullv note its color. 



