hybrids to the original form by the repeated employment of
its pollen; the value of these experiments for theoretical
purposes was afterwards fully brought out by Nageli.
It is impossible to rate too highly the general speculative value of Koelreuter's artificial hybridisation. The mingling of the characters of the two parents was the best refutation of the theory of evolution, and supplied at the same time profound views of the true nature of the sexual union. It was shown by his numerous experiments that only nearly allied plants and not always these are capable of sexual union, which at once disposed of Linnaeus' vague ideas in the judgment of every capable person, though it was long before science candidly accepted Koelreuter's results. The plant-collectors of the Linnaean school as well as the true systematists at the end of the 18th century had little understanding for such labours as Koelreuter's, and incorrect ideas on hybrids and their power of maintaining themselves prevailed in spite of them in botanical literature. Hybrids were necessarily in- convenient to the believers in the constancy of species; they. disturbed the compactness of their system and would not fit in with the notion that every species represented an ' idea.'
Koelreuter's doctrines however did not always fall on un- fruitful soil ; two botanists at least were found in Germany who adopted them, Joseph Gärtner the author of the famous Carpology and father of Carl Friedrich Gärtner who at a later time spent twenty-five years in experimenting on fertilisation and hybridisation, and Konrad Sprengel who took up Koelreuter's discovery of the services rendered by insects and arrived at some new and very remarkable results.
Joseph Gärtner made no fresh observations on sexuality himself, but in the Introduction to his 'De fructibus et seminibus plantarum' (1788) he made use of Koelreuter's results for the purpose of distinguishing more clearly between different kinds of propagation, and strengthening his own attack on the theory of evolution. The germ-grains or spores of cryptogamic
