Some flowers on these seedlings were then crossed with pollen taken from a distinct seedling, and other flowers were self-fertilised; two fresh lots of seedlings being thus raised, which were the grandchildren of the plant that had spread by stolons and formed a large clump in my garden. These differed much in height, the crossed plants being to the self-fertilised as 100 to 86. They differed, also, to a wonderful degree in constitutional vigour. The crossed plants flowered first, and produced exactly twice as many flower-stems; and they afterwards increased by stolons to such an extent as almost to overwhelm the self-fertilised plants.
Reviewing these five cases, we see that in four of them, the effect of a cross between flowers on the same plant (even on offsets of the same plant growing on separate roots, as with the Pelargonium and Origanum) does not differ from that of the strictest self-fertilisation. Indeed, in two of the cases the self-fertilised plants were superior to such intercrossed plants. With Digitalis a cross between the flowers on the same plant certainly did do some good, yet very slight compared with that from a cross between distinct plants. On the whole the results here arrived at, if we bear in mind that the flower-buds are to a certain extent distinct individuals and occasionally vary independently of one another, agree well with our general conclusion, that the advantages of a cross depend on the progenitors of the crossed plants possessing somewhat different constitutions, either from having been exposed to different conditions, or to their having varied from unknown causes in a manner which we in our ignorance are forced to speak of as spontaneous. Hereafter I shall have to recur to this subject of the inefficiency of a cross between the flowers on the same plant, when we consider the part which insects play in the cross-fertilisation of flowers.
ON THE TRANSMISSION OF THE GOOD EFFECTS FROM A CROSS AND OF THE EVIL EFFECTS FROM SELF-FERTILISATION.
We have seen that seedlings from a cross between distinct plants almost always exceed their self-fertilised opponents in height, weight, and constitutional vigour, and, as will hereafter be shown, often in fertility. To ascertain whether this superiority would be transmitted beyond the first generation, seedlings were raised on three occasions from crossed and self-fertilised plants, both sets being fertilised in the same manner, and therefore not as in the many cases given in Tables 7/A, 7/B, 7/C, in which the crossed plants were again crossed and the self-fertilised again self-fertilised.
Firstly, seedlings were raised from self-fertilised seeds produced under a net by crossed and self-fertilised plants of Nemophila insignis; and the latter were to the former in height as 133 to 100. But these seedlings became very unhealthy early in life, and grew so unequally that some of them in both lots were five times as tall as the others. Therefore this experiment was quite worthless; but I have felt bound to give it, as opposed to my general conclusion. I should state that in this and the two following trials, both sets of plants were grown on the opposite sides of the same pots, and treated in all respects alike. The details of the experiments may be found under the head of each species.
Secondly, a crossed and a self-fertilised plant of Heartsease (Viola tricolor) grew near together in the open ground and near to other plants of heartsease; and as both produced an abundance of very fine capsules, the flowers on both were certainly cross-fertilised by insects. Seeds were collected from both plants, and seedlings raised from them. Those from the crossed plants flowered in all three pots before those from the self-fertilised plants; and when fully grown the former were to the latter in height as 100 to 82. As both sets of plants were the product of cross-fertilisation, the difference in their growth and period of flowering was clearly due to their parents having been of crossed and self-fertilised parentage; and it is equally clear that they transmitted different constitutional powers to their offspring, the grandchildren of the plants which were originally crossed and self-fertilised.