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Show 284 SUM:MARY OF M:EASUREM:ENTS. CHAP. VII. column, that of the crosseJ plants being taken as ~00. A few. other cases have already boen recorded tn Table C In reference to plants crossed by a fresh stock. I regret that more trials of this kind were not 1nade, as the evidence of the superiority of tho crossed over the self-fertilised plants is thus shown in a more co~1clusive manner than by their relative heights. But this plan was not t?ough~ of .until a rather late period, and there were difficulties In the way, as tho seeds had to be collected wh~n ripe, by which ti1ne the plants had often begun to wither. In only one out of the eleven ~a.ses in ~rable B, that of Eschscholtzia, do the self-fertilised plants exceed the crossed in weight; and ~e h~ve already seen they are likewise superior to them In height, though inferior in fertility, the whole advant~ ge of a cross being here confined to tho reproductive ~ystem. vVith Vandellia the crossed plants were a httle heavier, as they were also a little taller than the self-fertilised ; but as a greater nu1nber of Inore productive capsules, were produced by tho cleistogene flowers on the self-fertilised plants than by those on the crossed plants, the case must Le left, as remarked under Table A, altogether doubtful. The crossed .and self-fertilised offspring fron1 a partially ~elf-s~enle plant of Reseda odorata wore almost equal ~~ we1ght, though not in height. In tho reJ11aining eight. c~ses, the crossed plants show a wonderful supenor1ty .over ~he self-fertilised, being more than double. th.mr we1ght, except in one case, and here the rat10 IS as high as 100 to 67. rfho results thus de~u~ed fron~ the weights of the plants confinu in a stnk1ng manner the fonner evidence of the beneficial effec~s of a cross between two plants of the smne stock ; and In .the few cases in whieh plants dorivccl from a c:o~s With a fresh stock were weighed, the results are Similar or even more striking. • CHAP. VIII. CONSTITUTIONAL VIGOUR. 285 CHAPTER VIII. DIFl!'ERENUE BETWEEN CROSSED AND SELF-FERTILISED PLANTS IN CONSTITUTIONAL VIGOUR AND IN OTHEH RESPECTS. Greater constitutional vigour of crossed plants-The effects of great crowding-Competition with other kincls of plants- Self-fertilised plants more liable to premature death-Crossed plantd generally flower before the self-fertilised-Negative effects of intcrcrossing flowers on the same plant-Cases de::3cribed-Transmission of the good effects of a cross to later generations-Effeds of crossin~ plants of closely related parentage-Uniform colour of the flowers on plants self-fertilised during several generations awl cultivated under similar condition::!. Greater constitutional Vigour of crossed Plants.-A.s in almost all my experiments an equal number of crossed and self-fertilised seeds, or more commonly seedlings just beginning to sprout, were planted on the opposite sideB of the same pots, they had to co1npete with one another; and the greater height, weight, and fertility of the crossed plants may be attributed to their possessing greater innate constitutional vigour. Generally the plants of the two lots whilst very young were of equal height; but afterwards the crossed gained insensibly on their opponents, and this shows that they possessed some inherent superiority, though not displayed at a very early period of life. There were, however, some conspicuous exceptions to the rule of the two lots being at first equal in height; thus the crossed seedlings of the broom ( Sarothcwnn~ts scoparius) when under three inches in height were more than twice as tall as the self-fertilised plants. |