They were classified by Morren under two heads,
according to their formation from one or more leaves. Monophyllous
pitchers obey the same law, viz.: that the upper side of the leaf has
become the inner side of the pitcher. Only one exception to this rule is
known to me. It is afforded by the pitchers of the banyan or holy
fig-tree, _Ficus religiosus_, but it does not seem to belong to the same
class as other pitchers, since as far as it has been possible to
ascertain the facts, these pitchers are not formed by a few leaves as in
all other cases, but by all the leaves of the tree.
In some cases pitchers are only built up of part of the leaf-blade. Such
partial malformations obey a rule, that is common to them and to other
foliar enations, viz.: that the side of the leaf from which they emerge,
is always their outer side. The inner surface of these enations
corresponds to the opposite side of the leaf, both in color and in
anatomical structure. The last of the four rules above mentioned is
[245] that of the homologous variability. It asserts that the same
deviation may occur in different, but homologous parts of the same
plant. We have already dealt with some instances, as the occurrence of
the same pigment in the flowers and foliage, in the fruits and seeds of
the same plant, as also illustrated by the loss of the red or blue tinge
by flowers and berries.
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