150 HISTOLOGY OF MEDICINAL PLANTS 
LEAF PARENCHYMA 
The parenchyma cells (Plate 109, Fig. 1) of leaves, of flower 
petals, and the parenchyma cells. of some aquatic plants are 
branched; that is, each cell has more than two cell terminations. 
These cell terminations are frequently quite attenuated and 
usually very blunt. Such a cell structure provides for a greater 
amount of intercellular space and a maximum exposure of sur- 
face. This arrangement makes it possible for the parenchyma 
cells of the leaf to absorb more readily the enormous amount 
of carbon dioxide needed in the photosynthetic process. 
AQUATIC PLANT PARENCHYMA 
The parenchyma of aquatic plants (Plate 59) has large 
intercellular spaces formed by the chains of cells. 
WOOD PARENCHYMA 
Wood parenchyma (Plate 105, Fig. 3) cells are the narrowest 
parenchyma cells occuring in the plant. Their walls are always 
lignified and strongly pitted, and in some cases the end walls 
common to two cells are obliquely placed. 
PHLOEM PARENCHYMA 
Phloem parenchyma (Plate 100, Fig. 8) cells are usually 
associated with sieve cells. They are very long, narrow, and 
have thin, non-pitted walls. The thinness of the walls un- 
doubtedly enables the cells to conduct diffusible food substance 
more quickly than the cortical parenchyma cells. 
PALISADE PARENCHYMA 
Palisade parenchyma of leaves is of the typical parenchyma 
shape and the end walls are placed nearly on a plane, even 
when more than one layer is present. The cells are verv small, 
however, and the walls are very thin and non-pitted. 
