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Show 178 HETEROSTYLED TRIMORPHIC PLANTS. CHAP IV. many more seeds, and th.e illegitimately fertilised flowers are not quite so stenle. Omalis rosea.-Hildebrand possessed in a living state only the long-sty led form of this trimorphic Ohilian species.* The pollen -grains from the two sets of anthers differ in diameter as 9 to 7 · 5, or as 100 to 83. He has further shown that there is an analogous difference between the grains from tb e two sets of anthers of the same flower in five other species of Oxalis, besides those already described. The present species differs remarkably from the long-sty led form of the three species previously experimented on, in a n1uch larger proportion of the flowers setting capsules when fertilised with their own-form pollen. Hildebrand. fertilised 60 flowers with pollen from the mid-length stamens (of either the same or another flower), and · they yielded no less than 55 capsules, or 92 per cent. These capsules contained on an average 5 · 62 seeds; but we have no means of judging how near an approach this average inakes to that from flowers legitimately fertilised. He also fertilised 45 flowers with pollen from the shortest stamens, and these yielded only 17 capsules, or 31 per cent., containing on an average · only 2 · 65 seeds. We thus see that about thrice as many flowers, w heri fertilised with pollen frmn the mid-length ,stamens, produced capsules, and these contained twice as many seeds, as did the flowers ·fertilised with pollen from the shortest stainens. It thus appears (and we find some evidence of the same fact with 0. speciosa ), that the same rule holds good with Oxalis as with Lythrum salicar~a ; namely, that in any two unions, t.ae greater the Inequality in length between the pistils and sta1nens, or, * 'Monatsber. der Akad. der WiEs. Berlin,' 1866, p. 372. CHAP. IV. OXALIS, OTHER SPECIES OF. 179 which is the same thing, the greater the distance of the stigma fro1n the anthers, the pollen of which is used for fertilisation, the less fertile is the union_ whether judged by the proportion of flowers which set capsules, or by the average number of seeds per capsule. The rule cannot be explained in this case any more than in .that of Lythrum, by supposing t~at w~er~ver there IS greater liability to self-fertilisation, this IS checked by the union beino· rendered more sterile; . f?r e.xactly. the reverse occurs, 0 the liability to self-fertilisation being greatest in the unions between the pistils and stamens which approach each other the nearest, and these are the 1nore fertile. I 1nay add that. I also possessed soine long-styled plants of this species: one was covered by a net, and it set spontaneously ~ few capsules, though extremely few comrared WIth those produced by a plant growing by Itself, but exposed. to the visits of bees. With most of the species of Oxalis the short-styled form seems to be· the most sterile of the three fonns when these are illegiti1nately fertilised; and I will adcl two other cases to those already given. I fertilised 29 ~hort-sty led flowers of 0. compressa with pollen from the.u· own two sets of sta1nens (the pollen -o·rains of ~hiCh differ in dia1neter as 100 and 83), and 0 not one pr0duced a ~apsule. I formerly cultivated during several years the short-sty led form of a species purchased under the name of 0. Bowii (but I have son1e doubts whether it was rightly named), and fertilised ma~y fl?wers with their own two kinds of pollen, Which differ in di::uneter in the usual manner but never got a sinb()' le seed. On the other hand H' ilde-br an~ says tha. t the short-styled form of 0. ' Deppei, gro~~ng by itself, yields plenty of seed; but it is not positively known that this species is heterosty leu ; and N 2 |