In Pisum the hybrids, ebtained from the immediate crossing of two forms, have in all cases the same type, but their posterity, on the contrary, are variable and follow a definite law in their variations. In Hieracium according to the present experiments the exactly opposite phenomenon seems to be exhibited. Already in describing the Pisum experiments it was remarked that there are also hybrids whose posterity do not vary, and that, for example, according to Wichura the hybrids of Salix reproduce themselves like pure species. In Hieracium we may take it we have a similar case. Whether from this circumstance we may venture to draw the conelusion that the polymorphism of the genera Salix and Hieracium is connected with the special condition of their hybrids is still an open question, which may well be raised but not as yet answered.
