The pollen-grains from the short-styled flowers are certainly larger, but only in a slight degree, than those from the long-styled, namely, as 100 to 94 in diameter. The short-styled form, which grows in the Gardens at Kew, has never there produced fruit.

Forsythia viridissima appears likewise to be heterostyled; for Professor Asa Gray says that although the long-styled form alone grows in the gardens at Cambridge, U.S., the published figures of this species belong to the short- styled form.

Cordia [sp.?] (Cordiaceae).

Fritz Muller sent me dried specimens of this shrub, which he believes to be heterostyled; and I have not much doubt that this is the case, though the usual characteristic differences are not well pronounced in the two forms. Linum grandiflorum shows us that a plant may be heterostyled in function in the highest degree, and yet the two forms may have stamens of equal length, and pollen-grains of equal size. In the present species of Cordia, the stamens of both forms are of nearly equal length, those of the short-styled being rather the longest; and the anthers of both are seated in the mouth of the corolla. Nor could I detect any difference in the size of the pollen-grains, when dry or after being soaked in water. The stigmas of the long-styled form stand clear above the anthers, and the whole pistil is longer than that of the short-styled, in about the ratio of 3 to 2.

The stigmas of the short-styled form are seated beneath the anthers, and they are considerably shorter than those of the long-styled form. This latter difference is the most important one of any between the two forms.

Gilia (Ipomopsis) pulchella vel aggregata (Polemoniaceae).

Professor Asa Gray remarks with respect to this plant: "the tendency to dimorphism, of which there are traces, or perhaps rather incipient manifestations in various portions of the genus, is most marked in G. aggregata." (3/17. 'Proceedings of the American Academy of Arts and Sciences.' June 14, 1870 page 275.) He sent me some dried flowers, and I procured others from Kew. They differ greatly in size, some being nearly twice as long as others (namely as 30 to 17), so that it was not possible to compare, except by calculation, the absolute length of the organs from different plants. Moreover, the relative position of the stigmas and anthers is variable: in some long- styled flowers the stigmas and anthers were exserted only just beyond the throat of the corolla; whilst in others they were exserted as much as 4/10 of an inch. I suspect also that the pistil goes on growing for some time after the anthers have dehisced. Nevertheless it is possible to class the flowers under two forms. In some of the long-styled, the length of pistil to that of the short-styled was as 100 to 82; but this result was gained by reducing the size of the corollas to the same scale. In another pair of flowers the difference in length between the pistils of the two forms was certainly greater, but they were not actually measured. In the short-styled flowers whether large or small, the stigma is seated low down within the tube of the corolla. The papillae on the long-styled stigma are longer than those on the short-styled, in the ratio of 100 to 40. The filaments in some of the short-styled flowers were, to those of the long-styled, as 100 to 25 in length, the free, or unattached portion being alone measured; but this ratio cannot be trusted, owing to the great variability of the stamens. The mean diameter of eleven pollen-grains from long-styled flowers, and of twelve from the short-styled, was exactly the same. It follows from these several statements, that the difference in length and state of surface of the stigmas in the flowers is the sole reliable evidence that this species is heterostyled; for it would be rash to trust to the difference in the length of the pistils, seeing how variable they are. I should have left the case altogether doubtful, had it not been for the observations on the following species; and these leave little doubt on my mind that the present plant is truly heterostyled.

The Different Forms of Flowers on Plants of the Same Species Page 52

19th Century English Literature

Charles Darwin

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