d, and also as a
result of the operation of the law of inheritance. On the same
principles it is easy to understand the occasional presence of the
perfect in place of the rudimentary organs, as in _Dianthus_.

In some instances the assumption of a scale-like form by any organ is
attended by a change in texture, the organs becoming dry and scarious,
or fleshy. Moquin cites in illustration of the first phenomenon the
flower of a _Vicia_, in which the petals were thick and fleshy, like the
scales of a bulb; and of the second the leaves of a _Chrysanthemum_,
which were replaced by small, glossy scales, like those which invest
ordinary leaf-buds. Sometimes the entire flower is replaced by
accumulations of small, acute, green scales. Cases of this kind, wherein
the flowers of a pea and of the foxglove were replaced by collections of
small ovate green scales packed one over the other till they resembled
the strobile of a hop, have been already alluded to. Most of these
scales are represented as having had other accumulations of scales in
their axils.

Similar collections of scales may frequently be met with in the birch
and in the oak, and probably represent abortive leaf-buds. Other cases
of a like kind in _Gentiana Amarella_, where the scales are coloured,
are mentioned elsewhere.

In some kinds of _Campanula_ a similar change is not uncommon.

=Formation of hairs, spines, &c.=--The adventitious production of hairs
is likewise frequently due to an arrested growth, in some cases arising
from pressure impeding the proper development of the organ. In other
cases the formation of hair seems to accompany the diminished
development of some organ, as on the barren pedicels of the wig plant,
_Rhus Cotinus_. A similar production of hair may be noticed in many
cases where the development of a branch or of a flower is arrested, and
this occurs with especial frequency where the arrest in growth is due to
the puncture of an insect, or to the formation of a gall. In such cases
the hairs are mere excrescences from the epidermis.

Prickles differ but little from hairs save in their more woody texture,
but true spines or thorns are modifications either of a leaf or of a
branch. Their presence seems often dependent on the soil in which the
plants grow, or on other external circumstances.

They occur normally in the sepals of _Paronychia serpyllifolia_ and
other plants.

=Formation of glands.=--Under this name are associated a number o