Schinzia, which forms galllike swellings on the roots of rushes; Gymnosporangium, causing excrescences on juniper stems; numerous leaf Fungi such as Puccinia, Aecidium, Sep/one, &c., causing yellow, brown or black spots on leaves; or Ustilago in the anthers of certain flowers.
Again, the curious distortions on the stems of nettles attacked by the Aecidium form of the heteroecious Puccina (]aricis (see FUNGf for Heteroecism), or on maize stems and leaves attacked by Ustilago Maydis, or on the inflorescence of crucifers infested with Cystopus, &c., are not individually very destructive; it is the cumulative effects of numerous attacks or of extensive epidemics which eventually tell.
Phytophthora in potatoes., If, on the other hand, the irritating agent is local in its action, causing only a few cells to react, we have the various pimples, excrescences, outgrowths, &c., exhibited in such cases as Ustilago Maydis on the maize, various galls, witchesbrooms, &c.
The application of ordinary antiseptic powders to leaves inside which a Fungus, such as a Uredo or Ustilago, is growing can only result in failtire, and similarly if tobacco fumes, for instance, are applied when the insects concerned are hibernating in the ground beneath.
Ustilago, and filling a greenhouse with hydrocyanic acid gas when young insects are commencing their ravages, e.g.
Brown spots are characteristic of Phytophthora, Puccinia, &c., and black ones of Fusicladium, Ustilago, Rhytisma, &c. Both are common as advanced symptoms of destruction by Fungi and insects.
Fungus-galls on leaves and stems are exemplified by the pocket-plums caused by the Exoasceae, the black blistering swellings of Ustilago Maydis, the yellow swellings on nettles due to Aecidium, &c.
Brefeld regarded the promycelium as a kind of basidium, bearing lateral or terminal conidia (comparable to basidiospores), but since the number of basidiospores is not fixed, and the basidium has not yet assumed very definite morphological characters, Brefeld termed the group Hemibasidii, and regarded them as a halfway stage in the evolution of the true Basidiomycetes from Ph co Y Y mycetes, the Tilletia type leading to the true basidium (Autobasidium), the Ustilago type to the proto pm basidium, with lateral spores; but this p m view is based on very poor evidence, so that it is best to place these forms?p, c;,::, as a separate group, the Ustilaginales.
A, of Ustilago receptaculorum; of Tilletia Caries (X 460).
Endophytic parasites may be intracellular, when the fungus or its mycelium plunges into the cells and destroys their contents directly (Olpidium, Lagenidium, Sclerotinia, &c.), but they are far more frequently intercellular, at any rate while young, the mycelium growing in the lacunae between the cells (Peronospora, Uredineae) into which it may send short (Cystopus), or long and branched (Peronospora Calotheca) haustoria, or it extends in the middle lamella (Ustilago), or even in the solid substance of the cell-wall (Botrytis).
Dematophora necatrix on roots, Calyptospora Goeppertiana on stems, Ustilago Scabiosae in anthers, Claviceps purpurea in ovaries, &c. Associated with these relations are the specializations which parasites show in regard to the age of the host.