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.
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