180 STEMS 
ground stems, being the kind of underground stem most common 
among Grasses and weeds. Many wild plants, such as the Ferns, 
May Apple or Mandrake, Solomon’s Seal, Iris, Water Lily, and 
others, have rhizomes. (Fig. 156.) 
Fic. 156. — Rhizome of the Mandrake (Podophyllum), showing aérial 
shoot and two scars (a) left by previous shoots. 
One striking feature is the difference in the way that rhizomes 
and their aérial shoots respond to gravity and light. While their 
aérial shoots grow toward the light and away from the earth, the 
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