I tried in several ways the comparative vigour and powers of growth of the crossed and self-fertilised plants of this third generation.  Thus, four self-fertilised seeds which had just germinated were planted on one side of a pot, and after an interval of forty-eight hours, four crossed seeds in the same state of germination were planted on the opposite side; and the pot was kept in the hothouse.  I thought that the advantage thus given to the self-fertilised seedlings would have been so great that they would never have been beaten by the crossed ones.  They were not beaten until all had grown to a height of 18 inches; and the degree to which they were finally beaten is shown in Table 2/4.  We here see that the average height of the four crossed plants is 76.62, and of the four self-fertilised plants 65.87 inches, or as 100 to 86; therefore less than when both sides started fair.

Table 2/4.  Ipomoea purpurea (Third Generation, the self-fertilised plants having had a start of forty-eight hours).

Heights of Plants in inches: 

Column 1:  Number (Name) of Pot.

Column 2:  Crossed Plants.

Column 3:  Self-fertilised Plants.

Pot 3 :  78 4/8 :  73 4/8. 
Pot 3 :  77 4/8 :  53. 
Pot 3 :  73 :  61 4/8. 
Pot 3 :  77 4/8 :  75 4/8.

Total :  306.5 :  263.5.

Crossed and self-fertilised seeds of the third generation were also sown out of doors late in the summer, and therefore under unfavourable conditions, and a single stick was given to each lot of plants to twine up.  The two lots were sufficiently separate so as not to interfere with each other’s growth, and the ground was clear of weeds.  As soon as they were killed by the first frost (and there was no difference in their hardiness), the two tallest crossed plants were found to be 24.5 and 22.5 inches, whilst the two tallest self-fertilised plants were only 15 and 12.5 inches in height, or as 100 to 59.

I likewise sowed at the same time two lots of the same seeds in a part of the garden which was shady and covered with weeds.  The crossed seedlings from the first looked the most healthy, but they twined up a stick only to a height of 7 1/4 inches; whilst the self-fertilised were not able to twine at all; and the tallest of them was only 3 1/2 inches in height.

Lastly, two lots of the same seeds were sown in the midst of a bed of candy-tuft (Iberis) growing vigorously.  The seedlings came up, but all the self-fertilised ones soon died excepting one, which never twined and grew to a height of only 4 inches.  Many of the crossed seedlings, on the other hand, survived; and some twined up the stems of the Iberis to the height of 11 inches.  These cases prove that the crossed seedlings have an immense advantage over the self-fertilised, both when growing isolated under very unfavourable conditions, and when put into competition with each other or with other plants, as would happen in a state of nature.