an exact knowledge of the structure and fertility of the hybrids and the condition of their offspring through several generations no one can undertake to determine the possible influence exercised by hybridisation over the multiplicity of intermediate forms in Hieracium. The condition of the Hieracium hybrids in the range we are concerned with must necessarily be determined by experiments; for we do not possess a complete theory of hybridisation, and we may be led into erroneous conclusions if we take rules deduced from observation of certain other hybrids to be Laws of hybridisation, and try to apply them to Hieracium without further consideration. If by the experimental method we can obtain a sufficient insight into the phenomenon of hybridisation in Hieracium, then by the help of the experience which has been collected respecting the structural relations of the wild forms, a satisfactory judgment in regard to this question may become possible.
Thus we may express the object which was sought after in these experiments. I venture now to relate the very slight results which I have as yet obtained with reference to this object.
1. Respecting the structure of the hybrids, we have to record the striking phenomenon that the forms hitherto obtained by similar fertilisation are not identical. The hybrids H. præaltum ♀ × H. aurantiacum ♂ and H. Auricula ♀ x H. aurantiacum are each represented by two, and H. Auricula ♀ x H. pratense ♂ by three individuals, while as to the remainder only one of each has been obtained.
If we compare the individual characters of the hybrids with the corresponding characters of the two parent types, we find that they sometimes present intermediate structures,
