THE STEM. 
79 
Other forms of underground stems are— 
The Cokm (Fig. 119).—Here the base of the stem 
Fig. 119. 
is abruptly thickened just below the surface of the 
ground, so as to resemble a tuber. 
The Bulb (Fig. 120).—A mass of thickened, scale¬ 
like leaves growing from a flat or conical base. From 
the under side of this base, roots are given off. 
Fig. 121 shows a vertical section of the bulb. 
The Riiizoma.— A stem more or less covered by 
the soil, from the nodes of which buds are given off 
above and roots below (Fig. 122). 
Bull up a growing onion and find its root and 
stenL 
