172 A TEXTBOOK OF GENERAL BOTANY 

Fig.172. Ginger plant with enlarged storage 
rhizome. (X +) 

Fig. 173. Storage rhizome of ginger. (x 3) 
start than one grow- 
ing from a seed, and, 
moreover, the rhi- 
zome is already in ~ 
the ground, whereas 
the seed may never 
reach the soil. 
Some stems grow 
up in the air at first 
and then, after they 
become long, bend 
down until they reach 
the ground, where 
they take root and so 
produce new plants. 
Storage. Except 
when the roots or 
leaves are fleshy and 
especially modified 
for food storage the 
stem is usually the 
chief organ in which 
food is stored. In 
large plants, food is 
stored at certain sea- 
sons in considerable 
quantities in the pith 
rays and the wood 
parenchyma. 
Some stems are es- 
pecially modified for 
the storage of food. 
These are usually 
underground stems such as the rhizomes of ginger (Figs. 172, . 
173), the tubers of potatoes (Fig. 174), or the corms of aroids 
(Fig. 175). While most stems that are specialized for food 
