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.