They constitute a very large group, the described species, according to Cooke's Census of Fungi, numbering not less than 10,500, or at least 1,000 more than all the recorded species of Hymenomycetes. The plants are microscopic in size, and grow upon vegetable or animal substances. HYPHOMYCETES. With regard to the Hyphomycetes, Cooke takes the ground that in their internal relations to each other, and their external relations to the remaining orders, the Hyphomycetes are undoubtedly a well-defined and natural group, and should have place as such in a systematic work. It is a large order, containing nearly 5,000 species, mostly parasitic on dead animals and vegetable matter. The spores, termed conidia, are free, as in Hymenomycetes. The species are microscopic in size, and the hyphae are strongly developed. They have no hymenium and no true basidia, and are non-sexual in their reproduction. The four primary sections are the Mucedineae, or "white moulds;" the Dematieae, or "black moulds;" the Stilbea, with the hyphae or thread-like filaments pallid or brown, and densely cohering, and the Tubercularieae, with the hyphae densely compacted in wart-like pustules of somewhat gelatinous consistency. The divisions called Melanconieae, Sphaeropsideae, and Hyphomyceteae are not recognized in the Brefield system of classification as distinct groups. Massee and Cooke, with other mycologists, take exception to this omission and its implication, in their discussion of the subject, giving consistent reasons for the retention of these groups in systematic works. PHYCOMYCETES OR PHYSOMYCETES. As originally defined by Berkeley, this group was composed chiefly of the old typical Mucors and their allies, and was then termed Physomycetes. In the newer system of classification its original definition has been extended so as to include a number of groups somewhat dissimilar in their habits and characteristics, but "united under the conservating bond of a dimorphic reproduction," and the name has been changed to Phycomycetes. As at present recognized "the Phycomycetes are characterized by a unicellular mycelium, often parasitic on plants or animals, sometimes saprophytic, developed in the air or in water. Reproduction sexual or asexual." As thus interpreted, Phycomycetes includes the Mucoracei; the Peronosporaceae, or "rotting moulds;" the Cystopi, or "white rusts;" the Saprolegniaceae, or "fish moulds;" the Entomophthoraceae, or "insect moulds," together with a few minor groups of doubtful natural affinity. BIBLIOGRAPHY. Saccardo, P. A. "Sylloge Sphaeropsidearum et Melanconiearum," in Sylloge Fungorum. Vol. iii. Imp. 8vo. Padua, 1884. L. A. Crie. _Recherches sur les Pyrenomycetes inferieurs du group de Depazees._ 8vo. Paris, 1878. J. C. Corda. _Icones Fungorum._ Fol. 6 vol. Prague, 1837-'54. Bonorden. _Zur Kenntniss der Coniomyceten u. Cryptomyceten._ 4to. Halle, 1860. M. C. Cooke. _The Hyphomycetous Fungi of the United States._ 8vo. 1877.