rities just specified should have been inherited in the one
continent from one progenitor, and in the other from another progenitor;
and considering that the trees inhabit widely different stations, these
peculiarities can hardly be supposed to be of any special {282} service to
the two series in the Old and New Worlds; therefore these peculiarities
cannot have been naturally selected. Hence we are led to infer that they
have been definitely caused by the long-continued action of the different
climate of the two continents on the trees.

_Galls._--Another class of facts, not relating to cultivated plants,
deserves attention. I allude to the production of galls. Every one knows
the curious, bright-red, hairy productions on the wild rose-tree, and the
various different galls produced by the oak. Some of the latter resemble
fruit, with one face as rosy as the rosiest apple. These bright colours can
be of no service either to the gall-forming insect or to the tree, and
probably are the direct result of the action of the light, in the same
manner as the apples of Nova Scotia or Canada are brighter coloured than
English apples. The strongest upholder of the doctrine that organic beings
are created beautiful to please mankind would not, I presume, extend this
view to galls. According to Osten Sacken's latest revision, no less than
fifty-eight kinds of galls are produced on the several species of oak, by
Cynips with its sub-genera; and Mr. B. D. Walsh[702] states that he can add
many others to the list. One American species of willow, the _Salix
humilis_, bears ten distinct kinds of galls. The leaves which spring from
the galls of various English willows differ completely in shape from the
natural leaves. The young shoots of junipers and firs, when punctured by
certain insects, yield monstrous growths like flowers and cones; and the
flowers of some plants become from the same cause wholly changed in
appearance. Galls are produced in every quarter of the world; of several
sent to me by Mr. Thwaites from Ceylon, some were as symmetrical as a
composite flower when in bud, others smooth and spherical like a berry;
some protected by long spines, others clothed with yellow wool formed of
long cellular hairs, others with regularly tufted hairs. In some galls the
internal structure is simple, but in others it is highly complex; thus M.
Lucaze-Duthiers[703] has figured in the common ink-gall no less than seven
concentric layers, composed