Remedial Treatment. Owing to the economic importance of these fungi, mycologists in various parts of the world have carried out considerable work on their control. According to the methods of infection, this remedial treatment may be classed under the two heads—(i) Destruction of seed-borne spores by steeping in some fungicide; (ii) destruction of perennating mycelium in the seed. (i.) Many species are perpetuated by spores carried on the seed; these germinate and infect the host in the seedling stage (e.g., Ustilago Avenae, U. levis, U. bromivora, U. Jensenii, Tilletia levis, and T. Tritici); in fact, the majority of the species of economic importance are included in this group. The treatment recommended is to steep the seed in some fungicide which destroys the spores without materially affecting the germination of the seed. Of the many solutions tried, formalin and copper-sulphate have been most widely used; unfortunately, both, though effective as fungicides, impair the germinating-vitality of the seed. Successful trials have recently been made with other fungicides, one of the most promising being powdered copper-carbonate, first recommended by Darnell-Smith (1917; 1921). For particulars as to the methods of treatment, and a résumé of the effect of these three substances on the germination of wheat, see Neill (1923), who also gives a bibliography of recent experimental work in this connection. German chemists have since 1914 been experimenting with considerable success with various organic and inorganic compounds in connection with smut-control, excellent results being claimed for certain mercury-chlorinephenol derivatives sold under the trade names of “Uspulun,” “Germisan,” &c. Samples of some of these compounds are now available, and will be tried out in this laboratory with a view to ascertaining whether they are applicable under New Zealand conditions. (ii.) Other species are perpetuated by means of hibernating mycelium in the ovule (e.g., Ustilago striaeformis, U. Tritici). This mycelium remains quiescent until the seed germinates, when it grows with the growing - point of the host until the formation of the inflorescence, eventually replacing the ovule by a mass of spores. Needless to say, external treatment with a fungicide is useless as a control in this case, since it cannot reach and destroy the internal mycelium. Jensen (1888; 1889A) demonstrated by numerous experiments that if the seed were soaked for a few hours in cold water, then for a few minutes in hot water (53° C.); infection by Ustilago Avenae and “U. nuda” was prevented. Freeman and Johnson (1909) found by experimenting with Jensen's modified hot-water treatment that “Ustilago nuda” and U. Tritici could be entirely held in check. Their methods are summarized below:— For barley, soak in cold water for five hours; follow by soaking in hot water at a temperature of 52° C. for fifteen minutes. For wheat, soak in cold water for five hours; follow by soaking in hot water at 54° C. for ten minutes. The seed may afterwards be stored for some time without detriment. Germination is but slightly affected if the treatment is carefully carried out. Osner (1916) has shown that the hot-water treatment is also an efficient controllant of Ustilago striaeformis. It could also be used for all the cereal smuts, but the work entailed is such that most growers prefer the simpler chemical steeps.