=Mode of Life.= The Fungi have no chlorophyll, and are thus unable in any stage of their existence to assimilate carbon; they must therefore live as _saprophytes_ or _parasites_. There is, however, no strong line of demarcation between these; many Fungi commence as true parasites, but only attain their full development upon or in dead plants or animals (_Rhytisma_, _Empusa_). Many saprophytes may occasionally appear as parasites, and are then designated “_facultative parasites_” (_Nectria cinnabarina_, _Lophodermium pinastri_), in contradistinction to those which only appear as parasites, “_obligate parasites_” (Mildew, Brand-and Rust-Fungi, _Cordyceps_). The parasites which live on the surface of the host-plant are termed _epiphytic_ (Mildew, _Fusicladium_); and those living in its tissues are termed _endophytic_ (_Ustilago_, _Peronospora_). _Epizoic_ (_Oidium tonsurans_, _Laboulbenia_) and _endozoic_ Fungi (_Cordyceps_, _Entomophthora_), are distinguished, in the same manner, as those which live on the surface or in the interior of animals. The Fungi designated _pathogenic_ are especially those which produce disease in human beings and in animals. Most of the diseases of plants are attributed to the parasitic Fungi. These force their way into the host-plant by piercing the outer wall of the epidermis, as in the Potato-disease; or by growing in through the stomata, _e.g._ the summer generations of the Rust of Wheat; or they can only penetrate through a wound, _e.g. Nectria_. Some effect an entrance into the host-plant by the secretion of a poisonous matter or ferment, which softens and destroys the cell-walls (_Sclerotinia_). Some Yeast and Mould Fungi secrete ferments (enzymes), which, for example, convert cane-sugar into a sugar capable of fermentation. The relation of the parasitic Fungus to the host-plant is mainly of two kinds. In the one case, the cell-contents are destroyed, the protoplasm is killed, and the cellular tissue becomes discoloured and dies (_Peronospora_, _Armillaria mellea_, _Polyporus_); in the other case, the parasite has an irritating effect on the cellular tissue, whereby the affected organ grows more rapidly and becomes larger than normal, producing _hypertrophy_. Such malformations are termed _Fungi-galls_ (Mycocecidia); in this manner “witches’ brooms” are produced by _Æcidium_, “pocket-plum” by _Taphrina_, and other deformities by _Exobasidium_ and _Cystopus candidus_. This hypertrophy may either be produced by a vigorous cell-multiplication, which is most frequently the case, or by the enlargement of the individual cells (_Synchytrium_, _Calyptospora_). The relation between host and Fungus among the Lichens is of a very peculiar nature, termed “_symbiosis_.”