150 HISTOLOGY OF MEDICINAL PLANTS 



LEAF PARENCHYMA 



The parenchyma cells (Plate 109, Fig. i) 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. 



