— 234 — 
In correlation with these facts the polymorphism and the 
power to make hybrids are not the same in the three subgenera. 
The most polymorphic subgenus is Archieracium, of which probably 
most of the species are apogamic; the only two hybrids of this 
subgenus, mentioned in literature as obtained artificially by G. 
Mendel, have both H. umbellatum — the only non-apogamic 
species — as father"). The cytological researchs by S. Murbeck 
(1904, pp. 291—294) and H. O. Juel (1905, pp. 10—13) have given 
the explanation af these things. Murbeck has examined three 
species of the head-section Aurella (sub-section Vulgata and a group 
intermediate between Vulgata and Tomentosa) and found them 
parthenogenetic in the sense, that the eggcell becomes an embryo; 
Juel on the other hand has found, that the development of both 
pollen and eggcell in H. umbellatum is quite typical, just as im an 
ordinary plant of the Composite. These results correspond very 
well with the results of my castration experiments. 
With regard to the cytological development in species of the 
other two subgenera nothing is to be found in the literature, but 
Dr. O. Rosenberg’s examinations (which he will publish in his 
paper) agree very well with my results. Worth noticing is also, 
that G. Mendel”) points out, that A. auricula is the best species 
for making hybrids artificially and that all the offsprings of his 
crossings after removal of the anthers have been hybrids, while 
from H. aurantiacum as motherplant hybrids could not be raised. 
The subgenus Stenotheca has not before been used for any expe- 
riments at all; but I should think the species of this subgenus would 
behave as the other genera of Cichorieæ (Taraxacum excepted). 
It is natural, that such an easy method of examining plants 
with regard to their power to develop fruits without fertilisation as 
that of Raunkiær has caused, that many other botanists have 
repeated the experiments with Taraxacum and Hieracium. As 
to Hieracium we find a short remark by H. Zahn (1904, p. 
170), in which he mentions, that castration experiments with H. 
boreale Fr., ssp. obliquum Jord. have succeeded. According to E. 
Strasburger (1904, p. 117) I. B. Overton has also repeated 
the castration experiments with the positive result. Further O. 
Kirchner (1905, p. 87) says briefly, that he has castrated H. 
aurantiacum and has examined the castrated heads cytologically 
1) C. Correns (1905), pp. 234—235. 
2) C. Correns (1905), p. 230. 
