THE SEEDLING AND YOUNG PLANT 81 
formed in the cells of the leaves. The water, with salts in 
solution, coming from the soil, after it has been absorbed 
by the root-hairs, passes up the wood (xylem) of the 
roots and stem, through the vessels of the petioles and 
leaf-venation, and is finally distributed to the cells of 
the mesophyll; the substances formed in these cells then 
pass down by the phloém (sieve-tubes, &c.) of the vena- 
tion and leaf-stalk, and thence are distributed to other 
parts of the plant. 
Now let us look at the mesophyll which these vascu- 
lar bundles support and serve as conduits for. It con- 
sists of two distinct parts (fig. 22). Beneath the upper 
epidermis, the cells of which are fitted closely together 
without intercellular spaces and are devoid of chlorophyll 
corpuscles, there are one or two rows of vertical sausage- 
shaped cells, closely arranged like the wooden railings 
of a complete palisade—consequently they are termed 
the palisade cells. The lower moiety of the mesophyll, 
on the other hand, is composed of irregular cells with 
large intercellular spaces between them, and this loose, 
spongy tissue, as it is aptly called, abuts below on the 
lower epidermis. Both the palisade cells and those of 
the spongy tissue contain numerous chlorophyll cor- 
puscles, as said. 
This lower epidermis is worth a few minutes’ con- 
sideration. It, like the upper epidermis, is also com- 
posed chiefly of closely fitting cells devoid of chlorophyll 
corpuscles, excepting that here and there we notice pairs 
of smaller cells containing chlorophyll—each pair with a 
G 
