[Illustration: FIG. 99.--_Ustilago._ 1. Formation of brand-spores. 2. Germinating brand-spore of _U. perennans_. 3. Germinating brand-spore of _U. cardui_ (after Brefeld). 4. _U. filiformis. a_ A brand-spore with developed basidium; _b_ another, with a conidium; _c_ with two conidia; _d_ with two conidia placed diametrically opposite to each other; _e_, detached conidia which are growing into hyphæ.] [Illustration: FIG. 100.--_Tilletia tritici_: _a_ an ear of Wheat in which all the grains are attacked by Stinkbrand; _b_ a blighted corn surrounded by the chaff; _c_ a blighted corn grown together with a stamen; _d_ the same cut across; _e_ a brand-spore; _f_, _g_, _h_ germinating brand-spores; _i_ germinating conidia; _j_ the mycelium; _k_-_k_ brand-spore-forming mycelium-threads. (_c-h_ magnified 400 times; _i-k_ 300 times.)] The conidia (also called “sporidia”) of many species unite generally into an H-form (Figs. 97, 4; 100 h; 101, 4). This union in pairs does not, however, take place with a view to germination, there is no fusion of nuclei, and therefore in this “fusion” there is no sexual act. Order 1. =Ustilaginaceæ.= Conidiophores with transverse walls and lateral conidia.--_Ustilago_ (Fig. 99) generally developes its spores in the floral organs of its host-plant, the ovary or anthers, where they arise from hyphæ, and form a slimy mass which when mature becomes a black dust. To this order belong _U. avenæ_, parasitic on Oats, _U. hordei_ and _U. nuda_ (_U. jenseni_), on Barley; these are the usual cause of “Smut” on cereals. _U. hypodytes_ on straw of _Elymus_ and _Agropyrum_. _U. filiformis_ in the leaves of _Glyceria_. _U. caricis_ transforms the fruits of various species of _Carex_ into black, dusty balls. _U. violacea_ developes its violet spore-powder in the anthers of the Caryophyllaceæ. _U. tragopogonis_, transforms entire inflorescences of _Tragopogon_ into a black-violet mass. Among the largest are _U. grandis_, which causes the large swollen nodes in the stem of _Phragmites_, and the Maize Blight, _U. maydis_, which produces outgrowths about the size of a hand on the spadix of the Maize.