KOLREUTER 16 
Between 1760 and 1766 Joseph Gottleib Kélreuter 
carried out the first series of systematic experiments 
in plant hybridization which had ever been under- 
taken. These experiments not only established with 
certainty for the first time the fact that the seeds of 
plants are produced by a sexual process comparable 
with that known to occur in animals, but also led to a 
knowledge of the general behaviour of hybrid plants, 
which was scarcely bettered until Mendel made his 
observations a century afterwards. 
Kélreuter found that the hybrid offspring of two 
different plants generally took as closely after the 
plant which yielded the pollen as after that upon 
which the actual hybrid seed was born. Indeed, he 
found that it made little or no difference to the ap- 
pearance of the hybrid which of the parental species 
was the pollen-parent (male), and which the seed- 
parent (female)—that is to say, in the case of plants 
the result of reciprocal crosses is usually identical. 
Thus, for the first time it was definitely shown that 
the pollen-grain plays just as important a part in 
determining the characters of the offspring as does the 
ovule which the pollen-grain fertilizes. This was a 
wholly novel idea in Kélreuter’s time, and the fact was 
scarcely credited by his contemporaries. 
Kélreuter had no means of discovering that the 
contents of a single pollen-grain unite with the con- 
tents of a single ovule in fertilization. But he ascer- 
tained by experiments that more than thirty seeds 
might be made to ripen by the application of between 
fifty and sixty pollen-grains to the stigma of a par- 
II 
