Mendel's Experiments with Hieracium 381 



which closely embraces the pistil. As soon as the flower 

 opens, the stigma, already covered with pollen, protrudes. 

 In order to prevent self- fertilisation the anther-tube must 

 be taken out before the flower opens, and for this purpose 

 the bud must be slit up with a fine needle. If this 

 operation is attempted at a time when the pollen is mature, 

 which is the case two or three days before the flower opens, 

 it is seldom possible to prevent self-fertilisation ; for with 

 every care it is not easily possible to prevent a few pollen 

 grains getting scattered and communicated to the stigma. 

 No better result has been obtained hitherto by removing 

 the anthers at an earlier stage of development. Before 

 the approach of maturity the tender pistil and stigma are 

 exceedingly sensitive to injury, and even if they are not 

 actually injured, they generally wither and dry up after a 

 little time if deprived of their protecting investments. I hope 

 to obviate this last misfortune by placing the plants after 

 the operation for two or three days in the damp atmosphere 

 of a greenhouse. An experiment lately made with H. 

 Auricula treated in this way gave a good result. 



To indicate the object with which these fertilisation 

 experiments were undertaken, I venture to make some 

 preliminary remarks respecting the genus Hieracium. This 

 genus possesses such an extraordinary profusion of distinct 

 forms that no other genus of plants can compare with it. 

 Some of these forms are distinguished by special peculiarities 

 and may be taken as type-forms of species, while all the 

 rest represent intermediate and transitional forms by which 

 the type-forms are connected together. The difficulty in 

 the separation and delimitation of these forms has demanded 

 the close attention of the experts. Regarding no other 



fenus has so much been written or have so many and such 

 erce controversies arisen, without as yet coming to a 

 definite conclusion. It is obvious that no general under- 

 standing can be arrived at, so long as the value and 

 significance of the intermediate and transitional forms are 

 unknown. 



Regarding the question whether and to what extent 

 hybridisation plays a part in the production of this wealth 

 of forms, we find very various and conflicting views held 

 by leading botanists. While some of them maintain that 



