Life Histories of Cereal Sniuts. 67 



CHAPTER XI. 



Life Histories of the Cereal Smuts. — Introductory. 



Since the smuts are all parasitic in their nature and cause disease in quite 

 a number of our economic plants, investigations have been directed, not only 

 towards gaining a complete knowledge of their history, but also a practical 

 means of preventing their ravages. In order to control their course and 

 counteract their influence it is essential to have a knowledge of their life 

 history and mode of attack, how they gain a footing in the plant, how they 

 reach the stage when spores are produced, and how these spores behave until 

 the plant is again infected. 



The hrst step in working out their life history was taken when Prevost\ 

 at the beginning of the nineteenth century, established the fact that the spores 

 when placed in water germinated, and since then various investigators, 

 including Tulasne, Kuehn, De Bary, Fischer von Waldheim, and Brefeld, 

 have advanced our knowledge until at the present time Brefeld has followed 

 their history from spore to spore, and given us a complete account of some 

 of the more important smuts. Only the cereal smuts will be dealt with here, 

 on account of their economic importance, including those which occur in 

 wheat, oats, barley, and maize. In our wheat lields there are three which do 

 considerable damage, and require to be carefully attended to with the extension 

 of the wheat-growing area, viz., stinking smut or bunt {Tilletia tritici and 

 T. levis), loose smut {Ustilago tritici), and flag smut {Uroci/stis tritici). In 

 oats there is only the loose smut {Ustilago avenae), and in barley there are 

 the two species known respectively as naked and covered smut. In the one 

 case the smut is enclosed in a membrane which soon breaks, and the spores 

 are scattered as in loose smut {Ustilago nuda), while in the other the smut is 

 enclosed in the unbroken walls of the ovary, and generally remains solid 

 after maturity {Ustilago Tiordei). In maize there is only one smut Icnown 

 here, which is commonly called head smut, because it attacks the entire 

 head {Sorosporium reilianum), but this has so frequently been confounded 

 with the corn smut so common in America that an account of the latter is 

 also given. A great deal still remains to be done before anything like a 

 complete account can be given of the Ufe histories of the various Australian 

 smuts ; still a beginning has been made, and when the gaps are known it may 

 lead to their being filled up all the sooner. 



In order to give a connected view of the cereal smuts and their different 

 peculiarities, I have arranged them in tabular form, and one of the most 

 striking features is that they naturally resolve themselves into two gi-oups, 

 according to their mode of infection — flower infection and seedling infection. 

 Among the flower infection forms there are only two, the loose smut of wheat 

 and the naked smut of barley. Both give rise directly to a mycelium on 

 germination without the formation of conidia, and the spores are scattered 

 naturally at the flowering season. 



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