Such tests have
been made by various experimenters. In the dandelion the bracts of the
involucre give the best characters. The inner ones may be linear or
linear-lanceolate, with or without appendages below the tip; the outer
ones may be similar and only shorter, or noticeably larger, erect,
spreading or even reflexed, and the color of the involucre may be a pure
green or glaucous; the leaves may be nearly entire or pinnatifid, or
sinuate-dentate, or very deeply runcinate-pinnatifid, or even pinnately
divided, the whole plant being more or less glabrous.
Raunkiaer, who has studied experimentally a dozen types from Denmark,
found them constant, but observed that some of them have no pollen at
all, while in others the pollen, though present, is impotent. It does
not germinate on the stigma, cannot produce the ordinary tube, [61] and
hence has no fertilizing power. But the young ovaries do not need such
fertilization. They are sufficient unto themselves. One may cut off all
the flowers of a head before the opening of the anthers, and leave the
ovaries untouched, and the head will ripen its seeds quite as well. The
same thing occurs in the hawkweeds. Here, therefore, we have no
fertilization and the extensive widening of the variability, which
generally accompanies this process is, of course, wanting.
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