118 A TEXTBOOK OF GENERAL BOTANY 

direction. They are living cells and contain a moderate amount 
of protoplasm. When they are exposed to the light they develop 
chloroplastids and are known as chlorenchyma cells. Chloren- 
chyma cells are thus only a special kind of parenchyma cells. 
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Fig. 115. Longitudinal section of a portion of a stem of Aristolochia elegans 
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e, epidermis ; c, cortex; co, collenchyma ; cl, chlorenchyma; p, pericycle ; sc, 
sclerenchyma ; pa, parenchyma; ph, phloém; st, sieve tube ; cc, companion cell ; 
ca, cambium ; x, xylem ; pv, pitted vessel ; av, annular vessel ; sv, spiral vessel ; 
pi, pith. (x 190) 
The parenchyma cells in the cortex of a stem are near enough 
to the light so that some or all of them develop chloroplastids 
and perform photosynthesis. 
By being distended with water (turgid), parenchyma cells 
frequently help in giving rigidity to an organ. This function 
of parenchyma cells is important in succulent stems and in 
the young parts of the stems of woody plants before strong 
