The different forms of flowers on plants of the same species, by Charles Darwin.
Kerner in his interesting essay (' Die Schutzmittel der Bliithen gegen unberufene Giste,' 1875, p. 19) insists that the petals of most plants contain matter which is offensive to insects, so that they are seldom gnawed, and thus the organs of fructification are protected. My grandfather in 1790 ('Loves of the Plants,' canto iii. note to lines 184, 188) remarks that "The flowers or petals of plants are perhaps in general more acrid than their leaves; hence they are much seldomer eaten by insects."