Chapter 7

SUMMARY OF THE HEIGHTS AND WEIGHTS OF THE CROSSED AND SELF-FERTILISED PLANTS.

Number of species and plants measured.
Tables given.
Preliminary remarks on the offspring of plants crossed by a fresh stock.
Thirteen cases specially considered.
The effects of crossing a self-fertilised plant either by another self-fertilised plant or by an intercrossed plant of the
old stock.
Summary of the results.
Preliminary remarks on the crossed and self-fertilised plants of the same stock.
The twenty-six exceptional cases considered, in which the crossed plants did not exceed greatly in height the self-fertilised.
Most of these cases shown not to be real exceptions to the rule that cross-fertilisation is beneficial.
Summary of results.
Relative weights of the crossed and self-fertilised plants.

The details which have been given under the head of each species are so numerous and so intricate, that it is necessary to tabulate the results. In Table 7/A, the number of plants of each kind which were raised from a cross between two individuals of the same stock and from self-fertilised seeds, together with their mean or average heights, are given. In the right hand column, the mean height of the crossed to that of the self-fertilised plants, the former being taken as 100, is shown. To make this clear, it may be advisable to give an example. In the first generation of Ipomoea, six plants derived from a cross between two plants were measured, and their mean height is 86.00 inches; six plants derived from flowers on the same parent-plant fertilised with their own pollen were measured, and their mean height is 65.66 inches. From this it follows, as shown in the right hand column, that if the mean height of the crossed plants be taken as 100, that of the self-fertilised plants is 76. The same plan is followed with all the other species.

The crossed and self-fertilised plants were generally grown in pots in competition with one another, and always under as closely similar conditions as could be attained. They were, however, sometimes grown in separate rows in the open ground. With several of the species, the crossed plants were again crossed, and the self-fertilised plants again self-fertilised, and thus successive generations were raised and measured, as may be seen in Table 7/A. Owing to this manner of proceeding, the crossed plants became in the later generations more or less closely inter-related.

In Table 7/B the relative weights of the crossed and self-fertilised plants, after they had flowered and had been cut down, are given in the few cases in which they were ascertained. The results are, I think, more striking and of greater value as evidence of constitutional vigour than those deduced from the relative heights of the plants.

The most important table is Table 7/C, as it includes the relative heights, weights, and fertility of plants raised