With several of the species, as with Eschscholtzia, Reseda, Viola, Dianthus, Petunia, and Primula, both lots were certainly cross-fertilised by insects, and so it probably was with several of the others; but in some of the species, as with Nemophila, and in some of the trials with Ipomoea and Dianthus, the plants were covered up, and both lots were spontaneously self-fertilised. This also was necessarily the case with the capsules produced by the cleistogene flowers of Vandellia.
The fertility of the crossed plants is represented in Table 9/D by 100, and that of the self-fertilised by the other figures. There are five cases in which the fertility of the self-fertilised plants is approximately equal to that of the crossed; nevertheless, in four of these cases the crossed plants were plainly taller, and in the fifth somewhat taller than the self-fertilised. But I should state that in some of these five cases the fertility of the two lots was not strictly ascertained, as the capsules were not actually counted, from appearing equal in number and from all apparently containing a full complement of seeds. In only two instances in the table, namely, with Vandellia and in the third generation of Dianthus, the capsules on the self-fertilised plants contained more seed than those on the crossed plants. With Dianthus the ratio between the number of seeds contained in the self-fertilised and crossed capsules was as 125 to 100; both sets of plants were left to fertilise themselves under a net; and it is almost certain that the greater fertility of the self-fertilised plants was here due merely to their having varied and become less strictly dichogamous, so as to mature their anthers and stigmas more nearly at the same time than is proper to the species. Excluding the seven cases now referred to, there remain twenty-six in which the crossed plants were manifestly much more fertile, sometimes to an extraordinary degree, than the self-fertilised with which they grew in competition. The most striking instances are those in which plants derived from a cross with a fresh stock are compared with plants of one of the later self-fertilised generations; yet there are some striking cases, as that of Viola, between the intercrossed plants of the same stock and the self-fertilised, even in the first generation. The results most to be trusted are those in which the productiveness of the plants was ascertained by the number of capsules produced by an equal number of plants, together with the actual or average number of seeds in each capsule. Of such cases there are twelve in the table, and the mean of their mean fertility is as 100 for the crossed plants, to 59 for the self-fertilised plants. The Primulaceae seem eminently liable to suffer in fertility from self-fertilisation.
The following short table, Table 9/E, includes four cases which have already been partly given in the last table.
TABLE 9/E.--INNATE FERTILITY OF PLANTS FROM A CROSS WITH A FRESH STOCK, COMPARED WITH THAT OF INTERCROSSED PLANTS OF THE SAME STOCK, AND WITH THAT OF SELF-FERTILISED PLANTS, ALL OF THE CORRESPONDING GENERATION. FERTILITY JUDGED OF BY THE NUMBER OR WEIGHT OF SEEDS PRODUCED BY AN EQUAL NUMBER OF PLANTS.
Column 1: Name of plant and feature observed.
Column 2: Plants from a cross with a fresh stock.
Column 3: Intercrossed plants of the same stock.
Column 4: Self-fertilised plants.
Mimulus luteus--the intercrossed plants are derived from a cross between two plants of the 8th self-fertilised generation. The self-fertilised plants belong to the 9th generation: 100 : 4 : 3.
Eschscholtzia californica--the intercrossed and self-fertilised plants belong to the 2nd generation: 100 : 45 : 40.
Dianthus caryophyllus--the intercrossed plants are derived from self-fertilised of the 3rd generation, crossed by intercrossed plants of the 3rd generation. The self-fertilised plants belong to the 4th generation: 100 : 45 : 33.
Petunia violacea--the intercrossed and self-fertilised plants belong to the 5th generation: 100 : 54 : 46.