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Show 308 SIZE OF THE COROLLA. CHAP. VII. amara, Geranium sylvatioum, Myosotis, and Saz1,ia. On the other hand, as Von Mohl remarks, when a plant produces hermaphrodite flowers and others which are males owing to the more or less complete abortion of the female organs, the corollas of the males are not at all increased in size, or only exceptionally and in a slight degree, as in Acer. * It seems therefore probable that the decreased size of the female corollas in the foregoing cases is due to a tendency to abortion spreading from the stamens to the petals. vVe see how intimately these organs are related in double flowers, in which the stamens are readily converted into petals. Indeed some botanists believe that petals do not consist of leaves directly metamorphosed, but of 1netamorphosed stamens. That the lessened size of the corolla in the above case is in some manner an indirect result of the modification of the reproductive organs is supported by the fact that in Rhamnus catha?"ticus not only the petals but the green and inconspicuous sepals of the female have been reduced in size; and in the strawberry the flowers are largest in the 1nales, midsized in the hennaphrodites, and smallest in the fenlales. These latter cases,-the variability in the size of the corolla in some of the above species, for instance in the con11non thyme,-together with the fact that it never differs greatly in size in the two forms-make n1e doubt much whether natural selection has come into play ;-that is whether, in accordance with H. 1\iiiller's belief, the advantage derived from the polleniferous flowers being visited first by insects has been sufficient to lead to a gradual reduction of the corolla of the female. We should bear in n1ind that as the hermaphrodite is the norn1al form, its corolla has * 'Bot. Zeitung,' 1863, p. 326. CHAP. VII. SIZE OF THE COROLLA. 309 probably retained its original size.* An objection to the above view should not be passed _over; namely, that the abortion of the stamens in the females ought to have added through the law of compensation to the size of the corolla; and this perhaps would have occurred, had not the expenditure saved by the a bortion _of the stamens been di:ected to the female reproductive organs, so as to g1ve to this form increased fertility. * It does not appear to me that Kerner's view ('Die Schutzmittel des Pollens,' 1873, p. 56) can be accepted in the present cases, namely that the larger corolla in the hermaphrodites and males s~rves to protect their pollen from ram. In the genus Thymus for instance, the aborted anther~ of the female are much better protected than the perfect ones of the hermaphrodite. |