Karl Friedrich von Gärtner (1772–1850) was cited extensively by Mendel (1865) for the former's view that species varied only within particular limits. Although interspecies hybrids were possible, Gärtner thought that they invariably reverted to type. According to Mendel, "Gärtner by the results of [his] transformation experiments, was led to oppose the opinion of those naturalists who dispute the stability of plant species and believe in a continuous evolution of plants. He perceives in the complete transformation of one species into another an indubitable proof that species are fixed within limits beyond which they cannot change. Although this opinion cannot be unconditionally accepted we find on the other hand in Gärtner’s experiments a noteworthy confirmation of that supposition regarding variability of cultivated plants which has already been expressed."

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