ters.

CHAPTER I.

PHYLLODY.

This condition, wherein true leaves are substituted for some other
organs,[245] must be distinguished from Virescence, q. v., in which the
parts affected have simply the green colour of leaves, without their
form or structure. The appearance of perfect leaves, in place of other
organs, is frequently looked on as due to retrograde metamorphosis, or
to an arrest of development. But this is not strictly correct; for
instance, suppose a petal, which is very generally merely the sheath of
a leaf, with the addition of colouring matter, to be replaced by a
perfect leaf, one in which all three constituent parts, sheath, stalk,
and blade, are present, it surely can hardly be said that there has been
any retrogression or arrest of development in the formation of a
complete in place of an incomplete organ. The term retrograde here is
used in a purely theoretical sense, and cannot be held to imply any
actual degradation. Morphologically, as has been stated, the case is one
of advance rather than the reverse, and hence the assignment of
instances of this nature to a perversion of development, rather than to
a diminution or to an exaltation of that process, seems most consistent
with truth. The affected organs have really undergone no actual change,
simply the direction of the organising force has been altered at a very
early state, so that the usual differentiation of parts has not taken
place.

[Illustration: FIG. 126.--'Rose plantain,' _Plantago media var._, spike
contracted; bracts leafy.]

=Phyllody of the bracts.=--As bracts are very generally imperfect
organs, so their replacement by perfect leaves is not attributable to
arrest of development or retrograde metamorphosis, but the reverse. The
bracts of some species of _Plantago_[246] are very subject to this
change. Thus, in the rose plantain of gardens, _P. media_ (fig. 126),
the bracts are leafy and the axis depressed or not elongated, so that it
is surmounted by a rosette of small leafy organs. A similar condition of
the bracts, unattended with arrest of growth in the axis, is common in
_P. major_ (fig. 127) and in _P. lanceolata_ (see p. 108). It also
occurs in the bracts of _Corydalis solida_, _Amorpha fruticosa_, _Ajuga
reptans_, _Parthenium inodorum_, _Centaurea Jacea_, in the involucral
bracts of the dandelion, the daisy, and many other composites. In the
'Gardeners Chronicle,' 1852, p. 579, is figured a dahlia in which the
b