— 946 — 



Die Luft scheint dieser Pflanze hier im Sommer zu trocken, viel- 

 leicht auch zu warm sein. Im Jahre 1870 waren die Mai- und 

 Juni-Blüthen ganz steril, im folgenden Jahre von theilweiser Frucht- 

 barkeit, die gegen den Herbst erschienenen einzelnen Köpfchen aber 

 vollkommen fruchtbar. Vermuthlich lag bei den Sommerblüthen die 

 Ursache der Sterilität in der schlechten Beschaffenheit des eigenen 

 Pollens, da es mir auch nicht gelingen wollte, mit demselben H. 

 auricula zu befruchten, während zu derselben Zeit die Befruchtung 

 mit dem Pollen der übrigen j^YoseZ/a-Varietäten keine Schwierigkeit 

 hatte. Gegen Ende August jedoch gelang eine Befruchtung mit 

 dem Pollen des H. pilosella, incanum". I have quoted Mendel's 

 words in extenso, as I think that he has mentioned just the points 

 which are of importance. The cause of the negative results of 

 Raunkiær's first castration experiment with Hieracium was, that he 

 used a H. pilosella-clump which, as we found by closer examination, 

 did not set fruits at all in the Botanical Garden. 



The same is the case with the H. umbellatum-stock in the 

 Garden and also with several other plants belonging to different 

 genera of Cichorieœ. 



The H. auricula mentioned above (Sériés VI,s) gave fruits in 

 the summer of 1905, while the heads of the autumn-scapes were 

 quite sterile. Some observations lead to the supposition, that it 

 perhaps will be possible to repress the fruiting power, when culti- 

 vating the specimens under dry conditions. 



(5) A phenomenon which at least in some respects is connected 

 herewith, is the obliteration of the pollen-grains. We have seen 

 that in H. excellens and H. roxolanicum, as they grow in the 

 Botanical Garden of Copenhagen, this obliteration is the ordinary 

 case. And Mendel (1870, p. 52) says, that it is not rare to find 

 a few flower-heads with empty anthers in wild-growing, quite 

 fertile species 1 ). 



Also H. Zahn (1904, p. 170) mentions, that female specimens 

 of a great number of Hieracium-species are not unusual, and 

 asserts, that they arise in some years rather numerously and 

 often under cultivation in gardens. I myself have also found, that 

 single specimens of a form of H. pilosella which grows abundantly 



r ) When Mendel thinks, that cross-fertilisation has taken place here, when 

 the purely female heads have given full fruits, he from his point of view- 

 is quite right; but now it is much more probable to suppose apogamy 

 here. 



