NUTRITIVE TISSUES 65 
95. In addition to the conducting and supporting 
systems, the remainder of the plant serves various 
functions. Thus, a large portion of green plants con- 
sists of nutritive tissues, These are usually found in 
leaves, but are also present in the younger parts of stems. 
In leaves we can usually distinguish, underneath the 
upper epidermis, one or more rows of closely packed 
cells, with their long axes perpendicular to the surface 
of the leaf, forming the so-called pali- 
sade parenchyma. In leaves equally 
lighted on both sides, this palisade 
parenchyma is often formed on both 
surfaces. Below the palisade layers 
the assimilative cells are looser, form- 
ing the “sponge”’ parenchyma, with Fia. 32.—Section of 
larger intercellular spaces between them, Rw 
which connect with the exterior through the stomata. 
96. The system of intercellular spaces is quite marked 
in all higher plants. These passages are usually con- 
Fic. 33.—Large intercellular spaces in water-lily petiole, and rush stem. 
tinuous through the petioles of the leaves into the stems 
and down into the roots. In plants growing in swampy 
places or in water these intercellular spaces are very 
much enlarged and apparently serve the double function 
of providing an ample air supply to the submerged por- 
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