If we now look down the right hand
column, in which the mean height, weight, and fertility of the plants
derived from a cross with a fresh stock are represented by 100, we shall
see by the other figures how wonderfully superior they are both to the
self-fertilised and to the intercrossed plants of the same stock. With
respect to height and weight, there are only two exceptions to the rule,
namely, with Eschscholtzia and Petunia, and the latter is probably no
real exception. Nor do these two species offer an exception in regard to
fertility, for the plants derived from the cross with a fresh stock were
much more fertile than the self-fertilised plants. The difference
between the two sets of plants in the table is generally much greater in
fertility than in height or weight. On the other hand, with some of the
species, as with Nicotiana, there was no difference in fertility between
the two sets, although a great difference in height and weight.
Considering all the cases in this table, there can be no doubt that
plants profit immensely, though in different ways, by a cross with a
fresh stock or with a distinct sub-variety. It cannot be maintained that
the benefit thus derived is due merely to the plants of the fresh stock
being perfectly healthy, whilst those which had been long intercrossed
or self-fertilised had become unhealthy; for in most cases there was no
appearance of such unhealthiness, and we shall see under Table 7/A that
the intercrossed plants of the same stock are generally superior to a
certain extent to the self-fertilised,--both lots having been subjected
to exactly the same conditions and being equally healthy or unhealthy.
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