In illustration of the very different estimates that have been made, however, may be mentioned that of De Bary in 1872 of 150,000 species, and that of Cooke in 1895 of 40,000, and Massee in 1899 of over 50,000 species, the fact being that no sufficient data are as yet to hand for any accurate census.
These forms are termed by Fischer Metatrophic, because they require various kinds of organic materials obtained from the dead remains of other organisms or from the surfaces of their bodies, and can utilize and decompose them in various ways (Polytrophic) or, if monotrophic, are at least unable to work them up. The true parasites - obligate parasites of de Bary - are placed by Fischer in a third biological group, Paratrophic bacteria, to mark the importance of their mode of life in the interior of living organisms where they live and multiply in the blood, juices or tissues.
It was not till De Bary (1866) made known the true nature of parasitic Fungi, based on his researches between 1853-1863, that the vast domain of epidemic diseases of plants was opened up to fruitful investigation, and such modern treatises as those of Frank (1880 and L895), Sorauer (1886), Kirchner (1890), were gradually made possible.
De Bary and others, while more recently, as cytology (q.v.), the intimate study of the cell and its contents has attracted considerable attention.
In 1876, however, Cohn had seen the spores germinate, and Koch, Brefeld, Pratzmowski, van Tieghem, de Bary and others confirmed the discovery in various species.
De Bary brought forward very strong evidence for the origin of the ascocarp in Sphaerotheca and Erysiphe by a sexual process, but Harper in 1895 was the first to prove conclusively, by the observation of the nuclear fusion, that there was a definite fertilization in Sphaerotheca Humuli by the fusion of a male (antheridial) nucleus with a female, ascogonial (oogonial) nucleus.