My v 
170 A TEXTBOOK OF GENERAL BOTANY 
primary one of the leaf. In addition, numerous stems are spe- 
cialized for photosynthesis and take the place of leaves in the 
manufactureofsugar. This 
is the case with the so-called 
asparagus fern and numer- 
ous sedges. Some stems 
which are specialized for 
photosynthesis are round 
(Figs. 43, 164, 167), others 
are flattened (Fig. 168), 
and others even have the 
form of leaves (Fig. 169). 
Such stems as those of the 
eacti (Figs. 512, 514) are 
specialized both for pho- 
tosynthesis and for water 
storage. 
Absorption (root func- 
tion). The epidermal walls 
of submerged water plants 
are not cutinized; conse- 
quently both the leaves and 
the stems of such plants— 
are capable of absorbing 
water and substances in 
solution in water. 
The stems of some para- 
sitic plants produce emer- 
Fig. 170. Cuscuta, a parasitic vine gences which enter the 
The stems produce haustoria that enter the tissues of the host and ab- 
] d absorb er rial. 
nost and a S01 water and food material sorb water and food mate- 
These haustoria are regarded as roots by 
some authorities.. (x 1) rial (Figs. 170, 171). 
The function of anchor- 
age, which is one of the chief functions of roots, is performed 
to some extent by underground stems (Fig. 172), as in cannas 
and many grasses. 









