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Show 202 PETUNIA VIOLACEA. CIIAP. VI. one lot being derived from plants self-fertilised for four generations and then crossed with a fresh stock; to the second lot being derived from plants of the same old stock intercrossed for five generations; and to the third lot being derived from plants selffertilised for five generations. All the capsules, some nearly mature and some only half-grown, were gathered, counted, and weighed from the ten finest plants in each of tho three rows, of which the measurements and weights have already been given. .The intercrossed plants, as we have seen, were taller and considerably heavier than the plants of the other two lots: and they produced a greater number of capsules than did even the ' Westerham-crossed plants; and this may be attributed to the latter having grown more crowded and being in consequence less branched. Therefore the average weight of an equal number of capsules from each lot of plants seems to be the fairest standard of comparison, as their weights will have been determined cpiefly by the number of the included seeds. As tho intercrossed plants were taller and heavier than the plants of the other two lots, it might have been expected that they woul9. have produced the finest or heaviest capsules; but this was very far from being the case. The ten tallest Westerham-crossed plants produced 111 ripe and unripe capsules, weighing 121· 2 grains. Therefore 100 of such capsules would have weighed 109 ·18 grains. The ten tallest intercrossed plants produced 129 capsules, weighing 76·45 grains. Therefore 100 of these capsulos .would have weighed 59 ·26 grains. The ten tallest self-fertilised plants produced only 44 capsules, weighing 22 · 35 grains. Therefore 100 of these capsules would have weighed 50·79 grains. From these data we get the following ratios for the fertility of the three lots, as deduced from the relative weights of an equal number of capsules from the finest plants in each lot:- Westerham-crossed plants to self-fertilised plants Wester ham-crossed plants to intorcrossed plants Intercrossed plants to self-fertilised plants as 100 to 46 as 100 to 54 as 100 to 86 We here see how potent the influence of a cross with pollen from a fresh stock has been on the fertility of plants self-fertilised fur four generations, in comparison with plants of the old stock when either intercrossed or self-fertilised for five generations; the CHAP. VI. COLOUR OF THE FLOWERS. 203 flowers on all these plants having been left to be freely crossed by insects or to fertilise themselves. The vVesterham-crossed plants were also much taller and heavier plants than the selffertilised, both in the pots and open ground; but they were less tall and heavy than the intercrossed plants. This latter result, however, would almost certainly have been reversed, if the plants had been allowed to grow for another month, as the vVesterham-crossed were still growing vigorously, whilst the intercrossed had almost ceased to grow. This case reminds us of the somewhat analogous one of Eschschol~zia, in which plants raised from a cross wjth a fresh stock did not grow higher than the self-fertilised or intercrossed plants, but produced a greater number of seed-capsules, which contained a far larger average number of seeds. Colour of the Flowers on tl,e above Tin ee Lots of Plants.-The origin~l mother-plant, from which the five successive self-fertili.sed generations were raised, bore dingy purple flowers. At no tn:r:e was any selection practised, and the plants were subjected In each generation to extremely uniform conditions. The result was, as in some previous cases, that the flowers on all the selffertilised plants, both in the pots and open ground, w~re absolutely uniform in tint; this being a dull, rather peculiar flesh colour. This uniformity was very striking in the long row of plants growing in the open ground, and the~c first attr.a~ted my attention. I did not notice in which generatiOn the ongmal colour began to change and to become uniform, but I have every reason to believe that the change was gradual. The flowers on the intercrossed plants were mostly of the same tint, but not nearly so uniform as those on the self-fertilised plants, and many of them were pale, approaching almost to white. The flowers on the plants from the cross with the purple-flowered Westerham stock were, as might have been expected, much more purple and not nearly Eo uniform in tint. The self-fertilised plants wer~ also remarkably uniform in height, as judged by the eye; t!1e Intercrossed less so whilst the V{esterham-crossed plants varied much in height. ' NICOTIANA TABACUM. This plant offers a curious case. Out of six trials ~ith crossed and self-fertilised plants, belonging to three successive g~ne~·ations, in one alone did the crossed show any marked supenonty in height over the self-fertilised ; in four of the trials they were |
