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.
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.