SHOOTS 
83 
STRUCTURE AND FUNCTION OF THE STEM 
57. Stem structure, The aerial foliage stem is the most 
favorable for studying stem structure, as it is not distorted 
by its position or by being a depository for food. If an 
active twig of an ordinary woody plant be cut across, it will 
FIG. 77. Flower clusters of an umbellifer (Sium). After STRASBTJRGER. 
be seen that it is made up of four general regions (see Fig. 
78): (1) an outer protecting layer, which may be stripped 
off as a thin skin, the epidermis ; (2) within the epider- 
mis a zone, generally green, the cortex ; (3) an inner zone 
of wood or vessels, known as the vascular region ; (4) a 
central pith. 
58. Dicotyledons and Conifers. Sometimes the vessels 
