tudinally, naturally
prolonged it to the end of the leaf. But the originating of varieties in
which the variegation did not assume this form, with other
considerations, has done much to upset this theory. In the variegated
leaved snowberry we have the center and border of the leaf green,
separated the one from the other by an isolated white or yellow zone. In
the zebra-leaved eulalia and the zebra-leaved juncus, from Japan, we
have the variegation of the leaf transversely instead of longitudinally,
so that according to the old theory we have the anomaly of a healthy
portion of the leaf producing an unhealthy portion, and that again a
healthy one, and thus alternately along the whole length of the leaf.

When we dissect a leaf in its primal development, we find that its cells
contain colorless globules, by botanists called chlorophyl or
phyto-color; these undergo changes according as they are acted upon by
light, oxygen, or other agents, producing green, yellow, red, and other
tints. This chlorophyl only exists in the outer or superficial cells of
the parenchyma or cellular tissue of the leaf, and thus differs from
starch and other substances produced in the internal cells, from which
the light is more or less excluded. It is a fatty or wax-like substance,
readily dissolved in alcohol or ether. The primal color of all leaves
and flowers is white or a pale yellowish hue, as can readily be seen by
cutting open a leaf or flower bud. The seed leaves of the French bean
are white when they come out of the earth, but they become green an hour
afterward under the influence of bright sunshine. A case is on record
where in a certain section, some miles in extent, in this country, about
the time of the trees coming into leaf, the sun did not shine for twenty
days; the leaves developed to nearly their full size, but were of a pale
or whitish color; finally, one forenoon the sun shone out fully, and by
the middle of the afternoon the trees were in full summer dress. These
facts show that the green color of leaves is due to the action of light.
Variegation is sometimes produced independently of the chlorophyl, as in
_Begonia argyrostigma_ and _Carduus marianus_, in which it is produced
by a layer of air interposed between the epidermis or outer skin of the
leaf and the cells beneath; this gives the leaf a bright, silvery
appearance.

To what, then, are we to ascribe leaf variegation? I think that it is
entirely due to diminished root