THE theory has long been prevalent among practical agriculturists that the proximity of berberry trees produces rust in wheat. Men of science, unable to trace herein the sequence of cause and effect, long derided the idea, and placed it among the prejudices of the agricultural mind. The facts of the farmer have, however, been too strong for the science of the botanist, and experience has won the day over theory. Let us trace for a moment the history of the inquiry. The first reference to the injurious influence of the berberry on corn appears in Krünitz's Encyclopædia, published in 1774. Marshall, in 1781, speaks of the berberry having been extirpated in Norfolk for this reason, and Schöpf, in 1788, mentions the same idea as prevalent in New England. Other writers of the same period give similar testimony; and in 1806 Sir Joseph Banks writes thus in the Annals of Botany:—“It has long been admitted by farmers, though scarcely credited by botanists, that wheat in the neighbourhood of a berberry bush seldom escapes the blight. The village of Rollesby, in Norfolk, where berberries abound, and wheat seldom succeeds, is called by the opprobrious appellation of ‘Mildew-Rollesby.’ Some observing men have lately attributed this very perplexing effect to the farina (pollen) of the flowers of the berberry, which is in truth yellow, resembling in some degree the appearance of the rust, or what is presumed to be the blight in its early state. It is, however, notorious to all botanical observers that the leaves of the berberry are very subject to the attacks of a yellow parasitic fungus, larger, but otherwise much resembling the rust in corn. Is it not more than possible that the parasitic fungus of the berberry and that of wheat are of the same species, and that the seed is transferred from the berberry to the corn?” The acute suggestion thrown out by Sir Joseph Banks, at a time when so little was accurately known of the structure of fungi, was not followed out for half a century; it was reserved for the German fungologist, De Bary, within the last few years to establish the truth of his theory, and to prove the existence of the phenomenon of Alternation of Generation among Fungi. The researches of Steenstrup and others have made us familiar with this remarkable phenomenon among the lower forms of animal life, but had hardly prepared us to meet with it in the vegetable kingdom. It appears probable, however, that the phenomenon is by no means uncommon here also,—affording another instance of the law that it is in their lowest forms that the animal and vegetable kingdoms approach one another most nearly,—and that whole tribes of fungi hitherto considered distinct are but different phases of one another. This remark applies especially to the two genera of minute parasitic fungi, Æcidium and Puccinia, to which the rusts in question belong, both belonging to the family Uredineœ. The well-known orange-red spots so common on the leaves of the berberry are produced by the Æcidium berberidis, while the rust of wheat and other cereal crops, but found equally on some other species of grass, as the common couch-grass or Triticum repens, is the Puccinia graminis. In the volume for 1865 of the Monatsberichte der kön. preuss. Akademie der Wissenschaften zu Berlin is a paper by Dr. De Bary, giving an elaborate account of his experiments on the propagation of these two fungi, in which, if his experiments are reliable, he clearly proves the correctness of Sir Joseph Banks's suggestion that they are one and the same species. The experiment was tried, with due precautions, of inoculating the leaves of the berberry with the spores of the Puccinia, the result being the production, not of the same fungus, but of the Æcidium, while the sowing of the spores of this latter fungus on the leaves of couch or wheat produced conversely the Puccinia. By sowing the spores of either fungus on the plant on which it was itself parasitic, he failed altogether to reproduce the same plant; and this alternation of generation may serve to account for the fact which has often been noticed, that rust is apt to appear not in successive but in alternate years on the same crop.