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Show 332 SELF-STERILE PLANTS. CnAP. IX. l\iuller in South Brazil happened to flower a month b.efore any of the others, and it did no~ produce a su~gle capsu l e. 1hI.S led hi'm to .m ake further ob~ervatwns d ur1. ng the nex t si·x ba enerations ' a. nd he found. that al• l hI.s p l an ts were cornpletely ste. nle. , unlfe ss, .they wme 1 . ,1 • h crossed by insects or were ar:Ificla~ly erti Iseu wit pollen froin a distinct plant, In "\Vhich. case the! were con1pletely fertile.* I was. much surpnsed at th1,s fact, as I had found that Enghsh plants, when covered by et Set a considerable nurnber of eapsules ; and that an, d ' hl these contained seeds by weight, compare wit t 1ose on plants intercrossed by the bees, as 7.1 to 1?0. Professor Hildebrand, however, found this species 1nuch more self-sterile in Germany than it was with me in England, for the capsules produc~d 1y selffertilised flowers, compared with those from Intercrossed flowers contained seeds in the ratio of only 11 to 100. At my' request Fritz Muller sent me from Brazil ~eeds of his self-sterile plants, fro1n which I raised soedhngs. Two of these were covered with a net, and one produced spontaneously only a single. capsule :~ntain~ng ~o good seeds, but yet, when artificially fertilised w1th 1ts own pollen, produced a few capsules. rrhe other plant prouucecl spontaneously under the net eight capsules, one of which contained no less than thirty seeds, and on an average a b out ten see d s per. capsul e . Eig·ht :flowers on these two plants were artificially self-fertilised, and produced seven capsules, conta·i·n ·i ng on an avera.ob ·e twelve seeds; e·i ght oth er fl ower.s wer·e fe-r·tilised WIth pollen frorn a distinct plant of the B raz1· 1·I an st oc k ' an.d produced eight capsules, containing on an avora~e. about ei• ghty see,u1 s: t h1' s gi·v es a rat 'IO of' 15 seeds for the self:-fertiliseu capsules to 100 for the crossct1 * 'Bot. Zeitung,' 1868, p. 115, and 1869, P· 223. CHAP. IX. SELF-STERILE PLANTS. 333 capsules. I_.ater in the season twelve other flowers on these two plants were artificially self-fertilised ; but they yielded only two capsules, containing three and six seed.s. It appears therefore that a lower temperature than that of Brazil favours the self-fertility of this plant, whilst. a still lower temperature lessens it. As· soon as the two plants which had been covered by the net were uncovered, they were visited by many bees, and it was interesting to observe how quickly they becan1e, even the In ore sterile plant of the two, covered with young capsules. On the following year eight flowers on plants of the Brazilian stock of selffertilised parentage (i.e., grandchildren of the plants which grew in Brazil) were again self-fertilised, and produced five capsules, containing on an average 27 ·4 seeds, with a maxi1nu1n in one of forty-two seeds; so that the~r self-fertility had evidently increased greatly by being reared for two generations in England. On the whole we may conclude that plants of the Brazilian stock are much rnore self-fertile in this country than in Brazil, and less so than plants of the English stock in England; so that the plants of Brazilian parentage retaine<l by inheritance some of their former sexual constitution. Conversely, seeds from English plants sent by me to Fritz Muller and grown in Brazil, were much more self.fertile than his plants whjch had been cultivated there for several generations; but he informs 1ne that one of the plants of English parentage which did not flower the first year, an<l was thus exposed for two seasons to the climate of Brazil, proved quite selfsterile, like a Brazilian plant, showing how quickly the climate had acted on its sexual constitution. Abutilon darwinii.-Seeds of this plant were sent me by Fritz lVIuller, who found it, as well as some other species of the same genus, quite sterile in its |
