to these public sources of information,
the author has availed himself of every opportunity that has offered
itself of examining cases of unusual conformation in plants. For many
such opportunities the author has to thank his friends and
correspondents. Nor has he less reason to be grateful for the
suggestions that they have made, and the information they have supplied.
In particular the writer is desirous of acknowledging his obligations to
the Society, under whose auspices this work is published, and to Mr. S.
J. Salter, to whom the book in some degree owes its origin.

The drawings, where not otherwise stated, have been executed either from
the author's own rough sketches, or from the actual specimens, by Mr. E.
M. Williams. A large number of woodcuts have also been kindly placed at
the disposal of the author by the proprietors of the 'Gardeners'
Chronicle.'[2]

As it is impossible to frame any but a purely arbitrary definition of
teratology or to trace the limits between variation and malformation, it
may suffice to say that vegetable teratology comprises the history of
the irregularities of growth and development in plants, and of the
causes producing them. These irregularities differ from variations
mainly in their wider deviation from the customary structure, in their
more frequent and more obvious dependence on external causes rather than
on inherent tendency, in their more sudden appearance, and lastly in
their smaller liability to be transmitted by inheritance.

What may be termed normal morphology includes the study of the form,
arrangement, size and other characteristic attributes of the several
parts of plants, their internal structure, and the precise relation one
form bears to another. In order the more thoroughly to investigate these
matters it is necessary to consider the mode of growth, and specially
the plan of evolution or development of each organ. This is the more
needful owing to the common origin of things ultimately very different
one from the other, and to the presence of organs which, in the adult
state, are identical or nearly so in aspect, but which nevertheless are
very unlike in the early stages of their existence.[3] Following Goethe,
these changes in the course of development are sometimes called
metamorphoses. In this way Agardh[4] admits three kinds of
metamorphosis, which he characterises as: 1st. Successive metamorphoses,
or those changes in the course of evolution which each in