On the other hand there are some red varieties of white-flowered species. But they are very rare, and little is known about their characters or constancy. Blue varieties of white species are not found. The yarrow (_Achillea Millefolium_) has a red-flowered form, which occurs [133] from time to time in sunny and sandy localities. I have isolated it and cultivated it during a series of years and during many generations. It is quite true to its character, but the degree of its coloring fluctuates between pink and white and is extremely variable. Perhaps it can be considered as an inconstant variety. A redflowered form of the common _Begonia semperflorens_ is cultivated under the name of "Vernon," the white hawthorn (_Crataegus Oxyacantha_) is often seen with red flowers, and a pink-flowered variety of the "Silverchain" or "Bastard acacia" (_Robinia Pseud-Acacia_) is not rarely cultivated. The "Crown" variety of the yellow wall-flower and the black varieties, are also to be considered as positive color variations, the black being due in the latter cases to a very great amount of the red pigment. Among fruits there are also some positive red varieties of greenish or yellowish species, as for instance the red gooseberry (_Ribes Grossularia_) and the red oranges. The red hue is far more common in leaves, as seen among herbs, in cultivated varieties of _Coleus_ and in the brown leaved form of the ordinary white clover, among trees and shrubs in the hazelnut (_Corylus_), the beech (_Fagus_), the birch (_Betula_), the barberry (_Berberis_) and many others. But though most of these forms are very ornamental and abundant [134] in parks and gardens, little is as yet known concerning the origin of their varietal attributes and their constancy, when propagated by seeds. Besides the ray-florets and the colors, there are of course a great many other characters in which varieties may differ from their species. In most of the cases it is easy to discern whether the new character is a positive or a negative one. And it is not at all necessary to scrutinize very narrowly the list of forms to become convinced that the negative form is the one which prevails nearly everywhere, and that positive aberrations are in a general sense so rare that they might even be taken for exceptions to the rule.