— 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 A. 
auricula zu befruchten, während zu derselben Zeit die Befruchtung 
mit dem Pollen der übrigen pilosella-Varietälen 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. wmbellatum-stock in the 
Garden and also with several other plants belonging to different 
genera of Cichoriew. 
The H. auricula mentioned above (Series VI,3) 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 A. 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"). 
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 HM. pilosella which grows abundantly 
1) 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. 
