the plum are numerous, and differ greatly in size,
shape, quality, and colour,--being bright yellow, green, almost white,
blue, purple, or red. There are some curious varieties, such as the
double or Siamese, and the Stoneless plum: in the latter the kernel
lies in a roomy cavity surrounded only by the pulp. The climate of
North America appears to be singularly favourable for the production of
new and good varieties; Downing describes no less than forty, seven of
which of first-rate quality have been recently introduced into
England.[689] Varieties occasionally arise having an innate adaptation
for certain soils, almost as strongly pronounced as with natural
species growing on the most distinct geological formations; thus in
America the imperial gage, differently from almost all other kinds, "is
peculiarly fitted for _dry light_ soils where many sorts drop their
fruit," whereas on rich heavy soils the fruit is often insipid.[690] My
father could never succeed in making the Wine-Sour yield even a
moderate crop in a sandy orchard near Shrewsbury, whilst in some parts
of the same county and in its native Yorkshire it bears abundantly: one
of my {347} relations also repeatedly tried in vain to grow this
variety in a sandy district in Staffordshire.

Mr. Rivers has given[691] a number of interesting facts, showing how
truly many varieties can be propagated by seed. He sowed the stones of
twenty bushels of the greengage for the sake of raising stocks, and
closely observed the seedlings; "all had the smooth shoots, the
prominent buds, and the glossy leaves of the greengage, but the greater
number had smaller leaves and thorns." There are two kinds of damson,
one the Shropshire with downy shoots, and the other the Kentish with
smooth shoots, and these differ but slightly in any other respect: Mr.
Rivers sowed some bushels of the Kentish damson, and all the
seedlings-had smooth shoots, but in some the fruit was oval, in others
round or roundish, and in a few the fruit was small, and, except in
being sweet, closely resembled that of the wild sloe. Mr. Rivers gives
several other striking instances of inheritance: thus, he raised eighty
thousand seedlings from the common German Quetsche plum, and "not one
could be found varying in the least, in foliage or habit." Similar
facts were observed with the