KOLREUTER 163 
stigma, or by the agency of the wind, or, lastly, the 
pollen may be carried by insects visiting the flowers. 
And he recognised many features characteristic of 
flowers apt to be fertilized in one or other of these 
ways in particular. Thus he was aware, for example, 
of the nature and use of the nectar which so many 
flowers produce—namely, that it is the substance from 
which the bees—by far the most diligent visitors of 
flowers—obtain their honey. 
Curiously enough, Kolreuter was not aware of the 
existence of any natural wild hybrid plants. But he 
was quite right in contending that supposed examples 
of such hybrids required for their substantiation the 
experimental proof, which could only be afforded by 
making actual artificial crosses between the putative 
‘parent species. 
The first hybrid made artificially by Kélreuter was 
obtained in 1760 by applying the pollen of Nicotiana 
paniculata to the stigma of Nicotiana rustica. The 
hybrid offspring of this cross showed a character inter- 
mediate between those of the two parent species in 
almost every measurable or recognisable feature, with 
a single notable exception. This exception was 
afforded by the condition of the stamens and of the 
pollen grains produced by the hybrids. These organs 
were so badly developed that in all the earlier experi- 
ments self-fertilization of the hybrid plants yielded no 
good seed at all, nor were the pollen grains of the 
hybrid any more effective when applied to the stigmas 
of either of the parent species. On the other hand, 
when pollen from either parent was applied to the 
II—2 
