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Show ) 330 SELF-S'rERILE PLANTS. CHAP, IX. ,'th tl at from a distinct plant; but it has been found WI 1 d' . . convenient to keep them for separate Iscussion. l110ie d d . h h The present cases must not be confoui~ e wit t ose to be given in the next chapter relatively to flowers ,,·hich are sterile when insects are excluded ; for s1:ch sterility depends not me~·ely o~ the flowers be1ng incapable of fertilisation ':Ith th~u own p~llen, but on 1nechanical causes, by which then pollen IS prevented fro1n reaching the stigma, or on the p~llen and s~igma of the same flower being matured at different ponods. . In the seventeenth chapter of my '-variation of Animals and Plants under Domestication' I had occasion to enter fully on the present subject; and I will therefore here give only a brief abstract of the cases there described, but others must be a lded, as they have an important bearing on the present work. Kolr~uter long ago described plants of Ver?ascu:n plue~weum which during two years were stenle with thou own pollen, but were easily fertilised by that of four other species; these plants however afterwards b.ecan1e more or less self-fertile in a strangely fluctuating manner. Mr. Scott also found that this species, as well as two of its varieties, were self-sterile, as did Gartner in the case of Verbascu1n nigrum. So it was. according to this latter author, with two plants of Lobelia fulgens, though the pollen and ovules of both were in ~n efficient state in relation to other species. Fi vo spec~es of Passiflora and certain individuals of a sixth species have been found sterile with their own pollen; but slight changes in their conditions, such as being grafted on another stock or a change of te1nperature, ronde~·ed them self-fertile. Flowers on a completely self-unpotent plant of Passijlora alata fertilised w~th pol~en from its own self-impotent seedlings were quite fertile. Mr. Scott, and afterwards Mr. Munro, found that some CHAP. IX. SELF-STERILE PLANTS. 331 species of Oncicliun1 and of lVIaxillaria cultivated in a hothouse in Edinburgh wore quite sterile with their own pollen; and l!'ritz Muller found this to be the case with a large number of Orchidaceous genera growing in their native home of South Brazil.* He also discovered that the pollen-masses of some orchids acted on their own stigmas like a poison; and it appears that Gartner formerly observed indications of this extraordinary fact in the case of so1ne other plants. Fritz Muller also states that a species of Bignonia and Taberntemontctna echinata are both sterile with their own pollen in their native country of Brazil. t Several A mary llidaceous and Liliaceous plants are in the same predica1nent. Hildebrand observed with care Corydalis cava, and found it co1npletely self-sterile; t but according to Caspary a few self-fertilised seeds are occasionally produced : Corydalis halltrtt' is only slightly self-sterile, and 0. intennedia not at all so.§ Inanother Fuinariaceousgenus, I-Iypecoum, Hildebrand observed II that IL grandiflor·un~ was highly self-sterile, whilst H. procumbens was fairly self-fertile. Thunbergia alata kept by me ·in a wann greenhouse was self-sterile early in the season, but at a later period produced many spontaneously self-fertilised fruits. So it was with Papaver vagum: another species, P. alpinun~, vvas found by Professor I-I. Hoffmann to be quite selfsterile excepting on one occasion ;,f whilst P. somniferun~ has been with 1ne always completely self-fertile. Eschscholtzia calijornica. - This species deserves a fuller consideration. A plant cultivated by Fritz * 'Bot. Zeitung,' 1868, p. 114. t Ibid. 1868, p. 6~6, aud 1870, p. 274. t 'Report of the International HOI't. Congress,' 1866. § 'Bot. Zeitung,' June 27,1873. II 'Jnhrb. ftir wis:::. Botanik,' B. vii. p. 4t>4. ~ ' Zur Speciesfragc,' 1875, p. 47. |