gitimate plants, and from trimorphic plants all three
illegitimate forms. These can then be properly united in a legitimate
manner. When this is done, there is no apparent reason why they
should not yield as many seeds as did their parents when legitimately
fertilised. But such is not the case. They are all infertile, in various
degrees; some being so utterly and incurably sterile that they did
not yield during four seasons a single seed or even seed-capsule. The
sterility of these illegitimate plants, when united with each other in
a legitimate manner, may be strictly compared with that of hybrids when
crossed inter se. If, on the other hand, a hybrid is crossed with either
pure parent-species, the sterility is usually much lessened: and so it
is when an illegitimate plant is fertilised by a legitimate plant. In
the same manner as the sterility of hybrids does not always run
parallel with the difficulty of making the first cross between the two
parent-species, so that sterility of certain illegitimate plants was
unusually great, while the sterility of the union from which they
were derived was by no means great. With hybrids raised from the same
seed-capsule the degree of sterility is innately variable, so it is in a
marked manner with illegitimate plants. Lastly, many hybrids are profuse
and persistent flowerers, while other and more sterile hybrids produce
few flowers, and are weak, miserable dwarfs; exactly similar cases occur
with the illegitimate offspring of various dimorphic and trimorphic
plants.

Altogether there is the closest identity in character and behaviour
between illegitimate plants and hybrids. It is hardly an exaggeration
to maintain that illegitimate plants are hybrids, produced within the
limits of the same species by the improper union of certain forms, while
ordinary hybrids are produced from an improper union between so-called
distinct species. We have also already seen that there is the closest
similarity in all respects between first illegitimate unions and first
crosses between distinct species. This will perhaps be made more fully
apparent by an illustration; we may suppose that a botanist found two
well-marked varieties (and such occur) of the long-styled form of the
trimorphic Lythrum salicaria, and that he determined to try by crossing
whether they were specifically distinct. He would find that they yielded
only about one-fifth of the proper number of seed, and that they behaved
in all th