. Darwinism; an exposition of the theory of natural selection, with some of its applications. Natural selection; Evolution. VII ON THE INFERTILITY OF CROSSES 157 style is long, the globular stigma appearing just in the centre of the open flower. In the other kind the stamens are long, appearing in the centre or throat of the flower, while the style is short, the stigma being situated halfway down the tube at the same level as the stamens in the other form. These two forms have long been known to florists as the "pin-eyed" and the "thrum-eyed," but they are called by Darwin
. Darwinism; an exposition of the theory of natural selection, with some of its applications. Natural selection; Evolution. VII ON THE INFERTILITY OF CROSSES 157 style is long, the globular stigma appearing just in the centre of the open flower. In the other kind the stamens are long, appearing in the centre or throat of the flower, while the style is short, the stigma being situated halfway down the tube at the same level as the stamens in the other form. These two forms have long been known to florists as the "pin-eyed" and the "thrum-eyed," but they are called by Darwin the long-styled and short-styled forms (see woodcut).. Long-styled form. Short-styled form. Fio. 17.—Primula veris (Cowslip). The meaning and use of these different forms was quite unknown till Darwin discovered, first, that cowslips and primroses are absolutely barren if insects are prevented from visiting them, and then, what is still more extraordinary, that each form is almost sterile when fertilised by its own pollen, and comparatively infertile when crossed with any other plant of its own form, but is perfectly fertile when the pollen of a long-styled is carried to the stigma of a short-styled plant, or vice versa. It will be seen, by the figures, that the arrangement is such that a bee visiting the flowers will carry the pollen from the long anthers of the short-sty led form to the stigma of the long-styled form, Avhile it would never reach the stigma of another plant of the short-styled Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Wallace, Alfred Russel, 1823-1913. London and New York, Macmillan and co.
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