30 A TEXTBOOK OF GENERAL BOTANY 
Chlorenchyma. The parts of the leaf that lie within the epi- 
dermis and between the veins are especially suited to carrying 
on photosynthesis. The cells in this part of the leaf contain — 
chloroplastids and are known as chlorenchyma cells (Fig. 17). 
Palisade chlorenchyma. The chlorenchyma is usually divided 
into two regions. ‘The portion near the upper surface is generally 
composed of elongated cells which are close together, with their 
longest axis perpendicular to the epidermis (igs. 17, 28, 35), 
| When we look at a section 
of a leaf, these cells have 
an appearance resembling 
a palisade, and they are 
called palisade cells or pal- 
tsade chlorenchyma. ‘The 
palisade chlorenchyma may 
consist of a single layer of 
cells or of two or more 
layers. ‘These cells, being 
near the upper surface of 
Fra. 19. Section of palisade of a leaf of the leaf, are in a favorable 
Hibiscus, cut parallel with the epider- position to receive sunlight, 
mis. (x 425) and their chief function is 
to carry on photosynthesis. 
Their elongated shape is favorable to this function, as the light 
in going through them does not pass through many cell walls. 
Between the palisade cells are small air spaces which are con- 
nected with larger spaces in the lower part of the leaf, and 
through these with the stomata in the lower epidermis. These 
air spaces make it possible for gases to diffuse to and from the 
palisade cells. In Fig. 19 is shown a section cut across the pali- 
sade layer in a plane perpendicular to the longest axis of the 
cells and parallel with the epidermis. This section shows very 
plainly the air spaces which extend up between the palisade cells. 
The cells of the chlorenchyma contain a large central vacuole 
and a thin layer of protoplasm lining the wall. The chloroplastids 
are embedded in this protoplasm and are close to the cell wall. 

