THE STEM 193 
A Sucker is a slender underground branch that arises either 
on aroot orastem. Root suckers are produced by roses, poplars, 
elms, etc. and arise as adventitious buds on the roots of these 
plants. Stem suckers are produced by peppermint and other 
mints, etc., arising from the axils of scaly leaves on the rhizome, 
— decurrent 
leaf base 
 _ gerial stem 
Fic. 123.—Portion of a sprouting potato tuber. (After Robbins.) 
or they may arise from wound tissue which has developed on 
sawed-oft branches or from old wood near the base of old trees. 
ExoGENoUsS AND ENDOGENOUS STEMS.—Exogenous stems are 
typical of Gymnosperms and Dicotyledons and can increase 
materially in thickness due to the presence of acambium. Such 
stems show differentiation into an outer bark cylinder and an 
inner or wood cylinder. Between the bark and the wood cylin- 
ders is a cambium. 
