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Show 264 SUMMARY OF MEASUREMENTS. CIIA.P. VII. for three generations were crossed with pollen from a fresh stock, and their offspring were grown in competition with plants of the· fourth self-fertilised generation. The crossed plants thus obtained were to the self-fertilised in height as 100 to 81, and in fe rtility (both lots being left to be naturally fertilised by insects) as 100 to 33. These same crossed plants were a] so to the offspring from the plants of the third self-fertilised generation crossed by the intercrossed plants of th~ corresponding generation, in height as 100 to 85, and in fertility as 100 to 45. vVe thus see what a great advantage the offspring fro1n a cross with a fresh stock had, not only over the self-fertilised plants of the fourth o·eneration but b ' over the offspring from the self-fertilised plants of the third generation, when crossed by the intercrossed plants of the old stock. (7.) Pisum sativum.--It has been shown under the head of this species, that the several varieties in this country almost invariably fertilise themselves, owing to insects rarely visiting the flowers; and as the plants have been long cultivated under nearly similar conuitions, we can understand wLv a cross between two individuals of the same variety does not do the least good to the offspring either in height or fertility. This case is almost exactly parallel with that of Mimulus, or that of the Ipo1n a nameJ. Hero; for in these two instances, crossing plants which had been self-fertilised for seven generations did not at all benefit the offspring. On the other hand, a cross between two varieties of the pea causes a marked superiority in the growth and vigour of the offspring, over the self-fertilis d plants of tho same varieties, as shown by two excellent observers. From my own CHAP. VII. TABLE C. 265 observations (not made with great care) the offspring from crossed varieties were to self-fertilised. plants in height, in one case as 100 to about 75, and. in a second case as 100 to 60. (8.) Lathyrus odorat·us.-The sweet-pea is in the same state in regard to self-fertilisation as the common pea; and we have seen that seedlings from a cross between two varieties, which differed in no respect except in the colour of their flowers, were to the self-fertilised seedlings from the same mother-plant in height as 100 to 80; and in the second generation as 100 to 88. Unfortunately I did not ascertain whether crossing two plants of the same variety failed to produce any beneficial effect, but I venture to predict such would be the result. (9.) Petunia viola.eea.-The intercrossed plants of the sa1ne stock in four out of the five successive gene; rations plainly exceeded in height the self-fertilised plants. The latter in the fourth generation were crossed by a fresh stock, and the seedlings thus obtained were put into competition with the self-fertilised plants of the fifth generation. The crossed plants exceeded the self-fertilised in height in the ratio of 100 to 66, and in weight as 100 to 23; but this difference, though so great, is not 1nuch greater than that between the intercrossed plants of the same stock in comparison with the self-fertilised plants of the corresponding generation. This case, therefore, seems at first sight opposed to the rule that a cross with a fresh stock is Inuch more beneficial than a cross between individuals of the same stock. But as with Eschscholtzia, the reproductive system was here chiefly benefited; for the plants raised fron1 the cross with the fresh stock were to the self-fertilised plants in fertility, both lots being naturally fertilised, as 100 to 46, whereas the |