n a yard in length, "twisting
about in all directions like a serpent." It is a singular fact that in
this latter variety many parts of the plant, namely, the stems, the
footstalks of the female flowers, the middle lobe of the leaves, and
especially the ovarium, as well as the mature fruit, all show a strong
tendency to become elongated. Several varieties of the melon are
interesting from assuming the characteristic features of distinct
species and even of distinct though allied genera: thus the
serpent-melon has some resemblance to the fruit of _Trichosanthes
anguina_; we have seen that other varieties closely resemble cucumbers;
some Egyptian varieties have their seeds attached to a portion of the
pulp, and this is characteristic of certain wild forms. Lastly, a
variety of melon from Algiers is remarkable from announcing its
maturity by "a spontaneous and almost sudden dislocation," when deep
cracks suddenly appear, and the fruit falls to pieces; and this occurs
with the wild _C. momordica_. Finally, M. Naudin well remarks that this
"extraordinary production of races and varieties by a single species,
and their permanence when not interfered with by crossing, are
phenomena well calculated to cause reflection."

USEFUL AND ORNAMENTAL TREES.

Trees deserve a passing notice on account of the numerous varieties
which they present, differing in their precocity, in their manner of
growth, foliage, and bark. Thus of the common ash (_Fraxinus
excelsior_) the catalogue of Messrs. Lawson of Edinburgh includes
twenty-one varieties, some of which differ much in their bark; there is
a yellow, a streaked reddish-white, a purple, a wart-barked and a
fungous-barked variety.[758] Of hollies no less than eighty-four
varieties are grown alongside each other in Mr. {361} Paul's
nursery.[759] In the case of trees, all the recorded varieties, as far
as I can find out, have been suddenly produced by one single act of
variation. The length of time required to raise many generations, and
the little value set on the fanciful varieties, explains how it is that
successive modifications have not been accumulated by selection; hence,
also it follows that we do not here meet with sub-varieties subordinate
to varieties, and these again subordinate to higher groups. On the
Continent, however, where the forests are