This chaotic state of things has brought some botanists to the conviction that even in systematic studies only direct experimental evidence can be relied upon. This conception has induced them to test the constancy of species and varieties, and to admit as real units only such groups of individuals as prove to be uniform and constant throughout succeeding generations. The late Alexis Jordan, of Lyons in France, made extensive cultures in this direction. In doing so, he discovered that systematic species, as a rule, comprise some lesser forms, which often cannot easily be distinguished when grown in different regions, or by comparing dried material. This fact was, of course, most distasteful to the systematists of his time and even for a long period afterwards [38] they attempted to discredit it. Milde and many others have opposed these new ideas with some temporary success. Only of late has the school of Jordan received due recognition, after Thuret, de Bary, Rosen and others tested its practices and openly pronounced for them. Of late Wittrock of Sweden has joined them, making extensive experimental studies concerning the real units of some of the larger species of his country. From the evidence given by these eminent authorities, we may conclude that systematic species, as they are accepted nowadays, are as a rule compound groups. Sometimes they consist of two or three, or a few elementary types, but in other cases they comprise twenty, or fifty, or even hundreds of constant and well differentiated forms. The inner constitution of these groups is however, not at all the same in all cases. This will be seen by the description of some of the more interesting of them. The European heartsease, from which our garden-pansies have been chiefly derived, will serve as an example. The garden-pansies are a hybrid race, won by crossing the _Viola tricolor_ with the large flowered and bright yellow _V. lutea_. They combine, as everyone knows, in their wide range of [39] varieties, the attributes of the latter with the peculiarities of the former species. Besides the _lutea_, there are some other species, nearly allied to tricolor, as for instance, _cornuta_, _calcarata_, and _altaica_, which are combined with it under the head of _Melanium_ as a subgenus, and which together constitute a systematic unity of undoubted value, but ranging between the common conceptions of genus and species. These forms are so nearly allied to the heartsease that they have of late been made use of in crosses, in order to widen the range of variability of garden-pansies. _Viola tricolor_ is a common European weed. It is widely dispersed and very abundant, growing in many localities in large numbers. It is an annual and ripens its seeds freely, and if opportunity is afforded, it multiplies rapidly.