One of them is the hawkweed or _Hieracium_, and the other is the dandelion or _Taraxacum officinale_. Hawkweeds are known as a genus in which the delimitation of the species is almost impossible, Thousands of forms may be cultivated side by side in botanical gardens, exhibiting [60] slight but undoubted differentiating features, and reproduce themselves truly by seed. Descriptions were formerly difficult and so complicated that the ablest writers on this genus, Fries and Nageli are said not to have been able to recognize the separate species by the descriptions given by each other. Are these types to be considered as elementary species, or only as individual differences? The decision of course, would depend upon their behavior in cultures. 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. Only partial or vegetative variability is present. Unfertilized eggs when developing into embryos are equivalent to buds, separated from the parent-plant and planted for themselves. They repeat both the specific and the individual characters of the parent. In the case of the hawkweed and the dandelion there is at present no means of distinguishing between these two contrasting causes of variability. But like the garden varieties which are always propagated in the vegetative way, their constancy and uniformity are only apparent and afford no real indication of hereditary qualities.