Linum flavum.

The pistil of the long-styled form of this species is nearly twice as long as that of the short-styled; the stigmas are longer and the papillae coarser. In the short-styled form the stigmas diverge and pass out between the filaments, as in the previous species. The stamens in the two forms differ in length; and, what is singular, the anthers of the longer stamens are not so long as those of the other form; so that in the short-styled form both the stigmas and the anthers are shorter than in the long-styled form. The pollen-grains of the two forms do not differ in size. As this species is propagated by cuttings, generally all the plants in the same garden belong to the same form. I have inquired, but have never heard of its seeding in this country. Certainly my own plants never produced a single seed as long as I possessed only one of the two forms. After considerable search I procured both forms, but from want of time only a few experiments were made. Two plants of the two forms were planted some way apart in my garden, and were not covered by nets. Three flowers on the long- styled plant were legitimately fertilised with pollen from the short-styled plant, and one of them set a fine capsule. No other capsules were produced by this plant. Three flowers on the short-styled plant were legitimately fertilised with pollen from the long-styled, and all three produced capsules, containing respectively no less than 8, 9, and 10 seeds. Three other flowers on this plant, which had not been artificially fertilised, produced capsules containing 5, 1, and 5 seeds; and it is quite possible that pollen may have been brought to them by insects from the long-styled plant growing in the same garden. Nevertheless, as they did not yield half the number of seeds compared with the other flowers on the same plant which had been artificially and legitimately fertilised, and as the short-styled plants of the two previous species apparently evince some slight capacity for fertilisation with their own-form pollen, these three capsules may have been the product of self-fertilisation.

Besides the three species now described, the yellow-flowered L. corymbiferum is certainly heterostyled, as is, according to Planchon, L. salsoloides. (3/6. Hooker's 'London Journal of Botany' 1848 volume 7 page 174.) This botanist is the only one who seems to have inferred that heterostylism might have some important functional bearing. Dr. Alefeld, who has made a special study of the genus, says that about half of the sixty-five species known to him are heterostyled. (3/7. 'Botanische Zeitung' September 18, 1863 page 281.) This is the case with L. trigynum, which differs so much from the other species that it has been formed by him into a distinct genus. (3/8. It is not improbable that the allied genus, Hugonia, is heterostyled, for one species is said by Planchon (Hooker's 'London Journal of Botany' 1848 volume 7 page 525) to be provided with "staminibus exsertis;" another with "stylis staminibus longioribus," and another has "stamina 5, majora, stylos longe superantia.") According to the same author, none of the species which inhabit America and the Cape of Good Hope are heterostyled.

I have examined only three homostyled species, namely, L. usitatissimum, angustifolium, and catharticum. I raised 111 plants of a variety of the first- named species, and these, when protected under a net, all produced plenty of seed. The flowers, according to H. Muller, are frequented by bees and moths. (3/9. 'Die Befruchtung der Blumen' etc. page 168.) With respect to L. catharticum, the same author shows that the flowers are so constructed that they can freely fertilise themselves; but if visited by insects they might be cross- fertilised. He has, however, only once seen the flowers thus visited during the day; but it may be suspected that they are frequented during the night by small moths for the sake of the five minute drops of nectar secreted. Lastly, L. Lewisii is said by Planchon to bear on the same plant flowers with stamens and pistils of the same height, and others with the pistils either longer or shorter than the stamens.

The Different Forms of Flowers on Plants of the Same Species Page 44

19th Century English Literature

Charles Darwin

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