Specimens were produced of the common red campion Lychnis diurnal, infested with a parasitic fungus allied to the “smut” in wheat, which fungus developes its fructification in the anthers of the flower. The campion, in its ordinary healthy state, has flowers bearing stamens only, or pistils only, but about half the plants infested with the parasitic fungus bear flowers with both stamens and pistils in the same flower. The writer had never seen bisexual flowers on healthy plants, and attributed the occurrence of that condition I the specimens produced to the presence of the parasitic fungus. The diseased plants very rarely produced capsules, but occasionally, late in the season, perfect capsules, bearing good seed, are found on them. A few of these flowers had been submitted to Mr. Charles Darwin, and he had suggested that the pollen being destroyed at an early period, the pistil was developed in compensation. But though this explanation appeared probable at first sight, further examination of the facts did not seem to sustain it. The writer believed the influence exerted by the pollen to be of a much more subtle and surprising character than this, and that instead of causing the development of a pistil in a plant that would have produced stamens only if left to itself, the fungus has the power to cause a plant which in its natural condition would have produced pistils only, to develope stamens for the accommodation of the parasites. She supposed that the spores of the fungus fell on the stigma of the flower, and infested all the seeds produced by that capsule; that of these, all the seeds which would naturally have produced plants bearing stamens only remain un affected in structure, but they have their pollen destroyed by it; that those which would naturally have produced pistils only develope these to a certain extent; but as the fungus which pervades the tissues of the campion cannot produce spores without anthers to fructify in, it compels the plant it inhabits to develope these for its accommodation, and the effort of so doing exhausts the forces of the plant, and causes the decay of the capsule, if indeed the previous stunting of the style does not prevent fertilization. The parasite comes like a cuckoo, establishes itself in the flower of the campion, and in order to nourish and find accommodation for the spores of the stranger its own offspring perishes. The production of health capsules late in the season may be accounted for by supposing that the vigour of the fungus becomes exhausted, and the pressure being removed the plant resumes its nature functions. The fact that only about half the diseased plants are bisexual favours the theory that the latter are female plants, in which the growth of stamens has been induced by the presence of the fungus.