Origin of Species in the Genus Hieracium. 349 
1. Species which require fertilisation, i.e., sexual species; 
2. Species which are partly apogamous; 
3. Absolutely apogamous species. 
Lately I have examined the pollen of a number of species and 
have found some interesting points with regard to its development. 
I have to premise that no observer has yet succeeded in obtaining 
germination of the pollen of Composite in artificial cultures 
(Molisch, Lidforss), nor have I myself succeeded. Therefore, when 
testing the germinative power of the pollen we can only observe 
whether any grains have germinated on the stigmas, or whether when 
laid in water or a solution of sugar, they throw off the exine at the 
points where the pollen-tubes should protrude. 1 have mostly used 
the latter method of investigation and have found that the few 
sexual species examined, H. venosum and H. staticifolium of the 
S/£//o///mf-subgenus, and H. umbellatum among the Archieracia, 
have quite normal pollen, all the grains being about equal in size, 
and in water showing the exine thrown off at the points indicated. 
Among the apogamous Archieracia some species have pollen which 
has degenerated into a few yellow-brownish lumps, and in these 
species the anthers look empty; hence these species are functionally 
female. In other species we find pollen consisting of grains very 
unequal in size, a greater or smaller number of them very small 
and evidently not fertile, while the rest are of the normal size and 
look fertile ; but they do not throw off the exine when laid in water, 
and I suppose that this pollen also is incapable of germination. 
Thus in the apogamous species where there is no use for the pollen, 
it is degenerate. Another question which I cannot answer, is 
whether or not the degeneration of the pollen preceded or has 
followed the acquisition of apogamy. 
The third and last sub-genus, Pilosella, stands between the two 
others as far as apogamy is concerned. Most of the species are 
apogamous, a few are sexual, but the apogamous ones are not 
absolutely apogamous, a fact that appears from the number of 
fertile seeds in castrated heads and from the power of hybridizing 
in many species. As far as my investigations go, the pollen is 
usually fertile, but I have not yet examined many species; and in 
some it has degenerated to brownish lumps or is wholly wanting. 
I have not found the intermediate stage which is so common in 
Archieracia, the Pilosella- species being either wholly hermaphrodite 
or purely female, 
