aspary as an argument against this plant being considered as an
ordinary hybrid produced from seed; but we should remember that with
hybrids the ovules have not been examined nearly so frequently as the
pollen, and they may be much oftener imperfect than is generally
supposed. Dr. E. Bornet, of Antibes, informs me (through Mr. J.
Traherne Moggridge) that with hybrid Cisti the ovarium is frequently
deformed, the ovules being in some cases quite absent, and in other
cases incapable of fertilisation.

* * * * *

Several theories have been propounded to account for the origin of _C.
adami_, and for the transformations which it undergoes. These
transformations have been attributed by some authors to simple
bud-variation; but considering the wide difference between _C.
laburnum_ and _purpureus_, both of which are natural species, and
considering the sterility of the intermediate form, this view may be
summarily rejected. We shall presently see that, with hybrid plants,
two different embryos may be developed within the same seed and cohere;
and it has been supposed that _C. adami_ might have thus originated. It
is known that when a plant with variegated leaves is budded on a plain
stock, the latter is sometimes affected, and it is believed by some
that the laburnum has been thus affected. Thus Mr. Purser states[904]
that a common laburnum-tree in his garden, into which three _grafts_ of
the _Cytisus purpureus_ had been inserted, gradually assumed the
character of _C. adami_; but more evidence and copious details would be
requisite to make so extraordinary a statement credible.

Many authors maintain that _C. adami_ is a hybrid produced in the
common way by seed, and that it has reverted by buds to its two
parent-forms. Negative results are of little value; but Reisseck,
Caspary, and I myself, tried in vain to cross _C. laburnum_ and
_purpureus_; when I fertilised the former with pollen of the latter, I
had the nearest approach to success, for pods were formed, but in
sixteen days after the withering of the flowers they fell off.
Nevertheless, the belief that _C. adami_ is a spontaneously produced
hybrid between these two species is strongly supported by the fact that
hybrids between these species and two others have spontaneously {390}
arisen. In a bed of seedli