pollen of the same form taken from a distinct plant, has now been given. The
results are seen in Table 1.12; the fertility being judged by two standards,
namely, by that of the proportional number of flowers which yielded capsules,
and by that of the average number of seeds per capsule. But for full accuracy
many more observations, under varied conditions, would be requisite.

With plants of all kinds some flowers generally fail to produce capsules, from
various accidental causes; but this source of error has been eliminated, as far
as possible, in all the previous cases, by the manner in which the calculations
have been made. Supposing, for instance, that 20 flowers were fertilised
legitimately and yielded 18 capsules, and that 30 flowers were fertilised
illegitimately and yielded 15 capsules, we may assume that on an average an
equal proportion of the flowers in both lots would fail to produce capsules from
various accidental causes; and the ratio of 18/20 to 15/30, or as 100 to 56 (in
whole numbers), would show the proportional number of capsules due to the two
methods of fertilisation; and the number 56 would appear in the left-hand column
of Table 1.12, and in my other tables. With respect to the average number of
seeds per capsule hardly anything need be said: supposing that the legitimately
fertilised capsules contained, on an average, 50 seeds, and the illegitimately
fertilised capsules 25 seeds; then as 50 is to 25 so is 100 to 50; and the
latter number would appear in the right hand column.

It is impossible to look at the above table and doubt that the legitimate unions
between the two forms of the above nine species of Primula are much more fertile
than the illegitimate unions; although in the latter case pollen was always
taken from a distinct plant of the same form. There is, however, no close
correspondence in the two rows of figures, which give, according to the two
standards, the difference of fertility between the legitimate and illegitimate
unions. Thus all the flowers of P. Sinensis which were illegitimately fertilised
by Hildebrand produced capsules; but these contained only 42 per cent of the