_Viola tricolor_ has three subspecies, which have been elevated to the rank of species by some authors, and which may here be called, for brevity's sake, by their binary names. One is the typical _V. tricolor_, with broad flowers, variously colored and veined with yellow, purple and white. It occurs in waste places on sandy soil. The second is called _V. arvensis_ or the field-pansy; it has small inconspicuous flowers, with pale-yellowish petals which are shorter than the sepals. It pollinates itself without the [40] aid of insects, and is widely dispersed in cultivated fields. The third form, _V. alpestris_, grows in the Alps, but is of lesser importance for our present discussion. Anywhere throughout the central part of Europe _V. tricolor_ and _V. arvensis_ may be seen, each occupying its own locality. They may be considered as ranging among the most common native plants of the particular regions they inhabit. They vary in the color of the flowers, branching of the stems, in the foliage and other parts, but not to such an extent as to constitute distinct strains. They have been brought into cultivation by Jordan, Wittrock and others, but throughout Europe each of them constitutes a single type. These types must be very old and constant, fluctuating always within the same distinct and narrow limits. No slow, gradual changes can have taken place. In different countries their various habitats are as old as the historical records, and probably many centuries older. They are quite independent of one another, the distance being in numerous cases far too great for the exchange of pollen or of seeds. If slow and gradual changes were the rule, the types could not have remained so uniform throughout the whole range of these two species. They would necessarily have split up into thousands [41] and thousands of minor races, which would show their peculiar characteristics if tested by cultures in adjacent beds. This however, is not what happens. As a matter of fact _V. tricolor_ and _V. arvensis_ are widely distributed but wholly constant types. Besides these, there occur distinct types in numerous localities. Some of them evidently have had time and opportunity to spread more or less widely and now occupy larger regions or even whole countries. Others are narrowly limited, being restricted to a single locality. Wittrock collected seeds or plants from as many localities as possible in different parts of Sweden and neighboring states and sowed them in his garden near Stockholm. He secured seeds from his plants, and grew from them a second, and in many cases a third generation in order to estimate the amount of variability. As a rule the forms introduced into his garden proved constant, notwithstanding the new and abnormal conditions under which they were propagated.