ngs from _C. elongatus_, which grew near to
_C. purpureus,_ and was probably fertilised by it, through the agency
of insects (for these, as I know by experiment, play an important part
in the fertilisation of the laburnum), the sterile hybrid _C.
purpureo-elongatus_ appeared.[905] Thus, also, Waterer's laburnum, the
_C. alpino-laburnum_,[906] spontaneously appeared, as I am informed by
Mr. Waterer, in a bed of seedlings.

On the other hand, we have a clear and distinct account given by M.
Adam, who raised the plant, to Poiteau,[907] showing that _C. adami_ is
not an ordinary hybrid. M. Adam inserted in the usual manner a shield
of the bark of _C. purpureus_ into a stock of _C. laburnum_; and the
bud lay dormant, as often happens, for a year; the shield then produced
many buds and shoots, one of which grew more upright and vigorous with
larger leaves than the shoots of _C. purpureus_, and was consequently
propagated. Now it deserves especial notice that these plants were sold
by M. Adam, as a variety of _C. purpureus_, before they had flowered;
and the account was published by Poiteau after the plants had flowered,
but before they had exhibited their remarkable tendency to revert into
the two parent-species. So that there was no conceivable motive for
falsification, and it is difficult to see how there could have been any
error. If we admit as true M. Adam's account, we must admit the
extraordinary fact that two distinct species can unite by their
cellular tissue, and subsequently produce a plant bearing leaves and
sterile flowers intermediate in character between the scion and stock,
and producing buds liable to reversion; in short, resembling in every
important respect a hybrid formed in the ordinary way by seminal
reproduction. Such plants, if really thus formed, might be called
graft-hybrids.

* * * * *

I will now give all the facts which I have been able to collect
illustrative of the above theories, not for the sake of merely throwing
light on the origin of _C. adami_, but to show in how many
extraordinary and complex methods one kind of plant may affect another,
generally in connection with bud-variation. The supposition that either
_C. laburnum_ or _purpureus_ produced by ordinary bud-variation the
intermediate and the other form, may, as already