Nearly all organs show differences. The most marked are those of the leaves, which may be small or large, linear or elliptic or oblong and even rhomboidal in shape, more or less hairy with simple or with stellate branched hairs, and finally of a pure green or of a glaucous color. The petals are as a rule obcordate, but this type may be combined with others having more or less broad emarginations at the summit, and with differences in breadth which vary from almost linear types to others which touch along their margins. The pods are short and broad, or long and narrow, or varying in sundry other [49] ways. All in all there are constant differences which are so great that it has been possible to distinguish and to describe large numbers of types. Many of them have been tested as to their constancy from seed. Jordan made numerous cultures, some of which lasted ten or twelve years; Thuret has verified the assertion concerning their constancy by cultures extending over seven years in some instances; Villars and de Bary made numerous trials of shorter duration. All agree as to the main points. The local races are uniform and come true from seed; the variability of the species is not of a fluctuating, but of a polymorphous nature. A given elementary species keeps within its limits and cannot vary beyond them, but the whole group gives the impression of variability by its wide range of distinct, but nearly allied forms. The geographic distribution of these elementary species of the whitlow-grass is quite distinct from that of the violets. Here predominant species are limited to restricted localities. Most of them occupy one or more departments of France, and in Holland two of them are spread over several provinces. An important number are native in the centre of Europe, and from the vicinity of Lyons, Jordan succeeded in establishing about fifty elementary [50] species in his garden. In this region they are crowded together and not rarely two or even more quite distinct forms are observed to grow side by side on the same spot. Farther away from this center they are more widely dispersed, each holding its own in its habitat. In all, Jordan has distinguished about two hundred species of _Draba verna_ from Europe and western Asia. Subsequent authors have added new types to the already existing number from time to time. The constancy of these elementary species is directly proven by the experiments quoted above, and moreover it may be deduced from the uniformity of each type within its own domain. These are so large that most of the localities are practically isolated from one another, and must have been so for centuries. If the types were slowly changing such localities would often, though of course not always, exhibit slighter differences, and on the geographic limits of neighboring species intermediates would be found. Such however, are not on record. Hence the elementary species must be regarded as old and constant types.