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Show 166 STERILITY. CHAP. XVJII. plants are eminently liable to this affection also seems to show _that it is in some manner caused by their unnatural treatment. In some mstances, as with Silene, Gartner's view seems the most probable, namely, that it is caused by an inherent tendency in the species to become dic:ecious. I can add another cause, namely, the illegitimate unions of reciprocally dimorphic or trimorphic plants, for I have observed seedlings of three species of Primula and of J,ythrurn saz~·caria, which had been raised from plants illegitimately fertilised by their own-form pollen, with some or all their anthers in a contabescent state. There is perhaps an additional cause, namely, self-fertilisation; for many plants of Dianthus and Lobelia, which bad been raised from self-fertilised seeds, had their anthers in this state; but these instances are not conclusive, as both genera are liable from other causes to this atiection. Cases of an opposite natme likewise occm, namely, piants with the female organs struck with sterility, whilst the male organs remain perfect. Dianthus Japonicus, a Passiflora, and Nicotiana, have been described by Gartner 85 as being in this unusual condition. Monstrosities as a cause of Sterility.-Great deviations of structure, even when the reproductive organs themselves are not seriously affected, sometimes cause plants to become sterile. But in other cases plants may become monstrous to an extreme degree and yet retain their full feTtility. Gallesio, who certainly had great experience,86 often attributes sterility to this en, use; but it may be suspected that in some of "his cases sterility ·was the cause, and not the result, of the monstrous growths. The cmious St. Valery apple, although it bears fruit, rarely produces seed. The wonderfully anomalous flowers of Begonia jl"igida, formerly described, though they appear fit for fructification, are sterile.8 7 Species of Primulre, in which the calyx is brightly coloured, are said 88 to be often sterile, though I have known them to be fertile. On the other hand, Verlot gives several cases of proliferous :flowers which can be propagated by seed. This was the case with a poppy, which had become monopetalous by the union of its petals.89 Another extraordinary poppy, with the stamens replaced by numerous small supplemenbry capsules, likewise reproduces itself by seed. This has also occurred with a plant of Saxifmga geurn, in which a series of adventitious carpels, bearing ovules on their margins, had been developed between the stamens and the normal carpels.90 Lastly, with respect to peloric flowers, which depart wonderfully from the natural structure,-those of Linaria vulga;ris seem generally to be more or less sterile, whilst those before described of Antirrhinum may"us, when artificially fertilised with their own pollen, are perfectly 85 ' Bastarderzeugung,' s. 356. 86 'Teoria della Riproduzione,' 1816, p. 81; 'Traite du Citrus,' 1811, p. 67. 87 Mr. 0. W. Crocker, in 'Gard. Chronicle,' 18Gl, p. 10!)2. ss Verlot, • Des Varietes,' 1865, p. 80. 89 V erlot, idem, p. 88. 90 Prof. Allman, Brit. Assoc., quoted in the ' Phytologist,' vol. ii. p. 483. Prof. Harvey, on the authority of Mr. Andrews, who discovered the plant, informed me that this monstrosity could be propagated by ·seed. With respect to the poppy, see Prof. Gocppert, as quoted in 'Journal of Horticulture,' July 1st, 1863, p. 171. I CHAP. XVIII. DOUBLE FLOWERS. 167 fertile, though sterile when left to themselves, for bees are unable to crawl into the narrow tubular :flower. The peloric flowers of Coryrlalis solida, according to Godron,91 are barren; whilst those of Gloxinia are well known to yield plenty of seed. In our greenhouse Pelargoniums, the central flower of the truss is often peloric, and Mr. Masters informs me that he tried in vain during several years to get seed from these :flowers. I likewise made many vain attempts, but sometimes succeeclecl in fertilising them with pollen from a normal :flower of another variety; and conversely I several times fertilised ordinary flowers with peloric pollen. Only once I succeeded in raising a plant from a peloric flower fertilised by pollen from a peloric flower borne by another variety; but the plant, it may be added, presented nothing particular in its structure. Hence we may conclude that no general rule can be laid down; but any great deviation from the normal structure, even when the reproductive organs themselves are not seriously affected, certainly often leads to sexual impotence. Double FloweTs.-When the stamens are converted into petals, the plant becomes on the male side sterile; when both stamens and pistils are thus changed, the plant becomes completely barren. Symmetrical flowers having numerous stamens and petals are the most liable to become double, as perhaps follows from all mulbple organs being the most subject to variability. But flowers furnished with only a few stamens, and others which are asymmetrical in structure, Rometimes bec0me double, as we see with the double gorse or Ulex, Petunia, and Antirrhinum. The Compositre bear what are called double flowers by the abnormal development of the corolla of their central :florets. Doubleness is sometimes connected with prolification,92 or the continued growth of the axis of the flower. Doubleness is strongly inherited. No one has produced, as Lindley remarks,93 double flowers by promoting the perfect health of the plant. On the contrary, unnatural conditions of life favour their production. There is some reason to believe that seeds kept during many yeaTS, and seeds believed to be imperfectly fertilised, yield double :flowers more freely than fresh and perfectly fertilised seed.94 Long-continued cultivation in rich soil seems to be the commonest exciting cause. A double narcissus and a double Anthemis nobilis, transplanted into very poor soil, have been observed to become single; 95 and I have seen a completely double white primrose rendered permanently single by being divided and transplanted whilst in full flower. It bas been observed by Professor Morren that doubleness of the :flowers and variegation of the leaves are antagonistic states; but so many exceptions to the rule have lately been recorded/6 that, though general, it cannot be looked at as invariable. 91 'Cumptes Rendus,' Dec. 19th, 1864, p. 1039. 9~ ' Gardcner·s Chronicle,' 1866, p. 681. 93 'Theory of Horticulture,' p. 333. 94 Mr. Fairweatl1er, in 'Transact. Hort. Soc.,' vol. iii. p. 40G; Bosse, qnoted by Bronn, 'Gescl!ichte der Natur,' B. ii. s. 77. On the effects of the re-moval of the anthers, see lVlr. Leitner, in Silliman's 'North American Journ. of Science,' vol. xxiii. p. 47; and Verlot, ' Des Yarietes,' 1865, p. 84. 9J Lindley's 'Theory of Horticulture,.' p. 333. 96 ' Gardener's Chronicle,' 18o5, p. 626; 1866, pp. 290, 730; and Verlot, 'Des Varietes,' p. 75. |