250 LEAVES 
Tn leaves having an oblique or vertical position, palisade tissue 
may be present also on the lower side. The spongy tissue, having 
fewer chloroplasts and so characterized on account of its loose 
structure, occupies the region between the palisade tissue and 
lower epidermis or the region between the palisade tissues when 
there is a lower palisade tissue present. It consists of cells irregu- 
Fig. 232. — Cross section of a Tomato leaf. e, upper epidermis; c, cuti- 
cle; p, palisade cells; s, spongy cells; d, lower epidermis; st, stoma; g, guard 
cells of the stoma; h, stomatal chamber; v, vein; w, parenchyma sheath of 
the vein. The small bodies shown in the palisade and spongy cells are the 
chloroplasts. 
lar in shape and so loosely joined as to provide a system of air 
spaces which extend in all directions reaching from the stomata 
into the palisade tissues. In function, which is the manufacture 
of food, the palisade and spongy mesophylls are identical. 
Structurally chlorenchyma cells are well adapted to their 
function. Their thin cellulose walls permit water and_ sub- 
stances in solution to pass in or out readily. They have proto- 
plasm, which, as in all living cells, is the substance endowed with 
life and, therefore, able to regulate its activities. The cytoplasm 
(the name applied to all of the protoplasm except the nucleus) 
only partially fills the cell cavity, forming only a peripheral 
layer. In this peripheral layer the nucleus and also the chloro- 
plasts are located. Such an arrangement of the protoplasm 
