364 Mendel's Experiments 



this phenomenon has a far-reaching influence, others, for 

 example, Fries, will have nothing to do with hybrids in 

 Hieracia. Others take up an intermediate position ; and 

 while granting that hybrids are not rarely formed between 

 the species in a wild state, still maintain that no great 

 importance is to be attached to the fact, on the ground 

 that they are only of short duration. The [suggested] 

 causes of this are partly their restricted fertility or complete 

 sterility; partly also the knowledge, obtained by experiment, 

 that in hybrids self-fertilisation is always prevented if pollen 

 of one of the parent-forms reaches the stigma. On these 

 grounds it is regarded as inconceivable that Hieracium 

 hybrids can constitute and maintain themselves as fully 

 fertile and constant forms when growing near their pro- 

 genitors. 



The question of the origin of the numerous and constant 

 intermediate forms has recently acquired no small interest 

 since a famous Hieracium specialist has, in the spirit of 

 the Darwinian teaching, defended the view that these 

 forms are to be regarded as [arising] from the trans- 

 mutation of lost or still existing species. 



From the nature of the subject it is clear that without 

 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 ex- 

 perience 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 



