With the nineteenth century, and the founding of the modern theories of nutrition by Ingenhousz, Priestley, and De Saussure, we find a new era started. As the discoveries of the microscopists continued to build up our knowledge of the anatomy of plants and began to elucidate the biology of the fungi and other cryptogams, while the chemists and physiologists laid the foundations of our modern science of plant life, it gradually became possible to tabulate and classify plant diseases, and discuss their symptoms and causes in a more scientific manner. Even in 1833, however, Turpin, and a far better observer, Unger, regarded parasitic fungi as due to diseased outgrowths of chlorophyll-corpuscles and parenchyma cells, views shared by Meyen (1837) and Schleiden (1846). We may pass over the various treatises of Wiegmann (1839), Meyen (1841), Raspail (1846), Kühn (1859), and a number of other works of the period, merely referring with emphasis to Berkeley's admirable papers in the _Gardener's Chronicle_ (1854) for a summary of what was then known. All these works antedate De Bary's _Morphologie und Physiologie der Pilze, etc._ (1866), in which he brought together the results of his researches during the decade, proving the real nature of parasitic diseases and infection as worked out by experiments between 1853 and 1863. This work put the whole subject of parasitic diseases of plants and animals on a new footing, and paved the way for the modern treatment of plant pathology as elaborated in the treatises of Frank (1880 and 1895), Sorauer (1886), Kirchner (1890), and others, to which the reader is referred for further details. I will merely quote the following passage from Raspail's _Histoire Naturelle de la Santé et de la Maladie_, 1846 (vol. ii., p. 176), in illustration of the views entertained by high authorities just prior to De Bary's work: "L'insecte qui produit les _erineum_, _uredo_, _æcidium_, _xyloma_, _puccinia_, n'est donc plus pour nous un insecte inconnu, mais un _acarus_ (grise), un _aphis_ (puceron) ou un _thrips_, qui produit au printemps une déviation, etc." And this view, that fungi already well known to mycologists were called forth by the punctures of insects, was regarded as not out of harmony with the idea that the fungus itself was an abnormal outgrowth of the tissues of the host.