but absolutely. This is often the case when
disease or injury affects the plant; for instance, in the case of galls
arising from insect-puncture the structure is rather a new growth
altogether, than dependent on mere hypertrophy of the original tissues.
These absolute deformities arising from the causes just mentioned belong
rather to pathology than to teratology strictly so called; but, under
the head of deformities, may be mentioned sundry deviations not
elsewhere alluded to.

CHAPTER I.

DEFORMITIES.

The special meaning here attached to the term deformity is sufficiently
explained in the preceding paragraph; it remains to give a few
illustrations, and to refer to other headings, such as Heterotaxy,
Hypertrophy, Atrophy, &c., for malformations capable of more rigid
classification than those here alluded to.

[Illustration: FIG. 166.--Portion of the under surface of a
cabbage-leaf, with horn-like excrescences projecting from it.]

=Formation of tubes.=--The production of ascidia or pitchers from the
cohesion of the margins of one or more leaves has been already alluded
to (see pp. 21, 30), but there is another class of cases in which the
tubular formation is due, not so much to the union of the margins of a
leaf as to the disproportionate growth of some portions as contrasted
with others, whence arises either a depressed cavity, as in the case of
a leaf, or an expanded and excavated structure, when the stem or some
portion of it is affected.

The fruit of the rose, the apple, the fig, and many others, is now
generally admitted to be composed externally of the dilated end of the
flower-stalk in which the true carpels become imbedded. Between such
cases and that of a peltate leaf with a depressed centre, such as often
occurs, to some extent, in _Nelumbium_, there is but little difference.

In cabbages and lettuces there not unfrequently occurs a production of
leaf-like processes projecting from the primary blade at a right angle
(see Enation). Sometimes these are developed in a tubular form, so as to
form a series of little horn-like tubes, or shallow troughs, as in
_Aristolochia sipho_. At other times the nerves or ribs of the leaf
project beyond the blade, and bear at their extremities structures
similar to those just described.

[Illustration: FIG. 167.--Lettuce leaf, bearing on the back a stalked
cup, arising from the dilatation of the stalk (?).]

In a variety of _Codiaeum variegatum_ a similar