Flail Sniitt of Wheat. 99 



nfectioii by diseased straw alone, as compared with spores on the (frain 

 was also tested in 1908. Two hundred grains of Federation were sown in four 

 divisions, the first having diseased straw added, and the other three had 

 the seed dusted with spores. The results were practically the same in each 

 case, as there were respectively 11, 13, 14, and 12 per cent, of Flag smut. 



There is a discrepancy here Ix'tween the results obtained by experiments 

 in pots and in the field, lor in the pots the diseased straw produced much 

 more severe infection than the spores. This may be due to the fact that 

 the regular watering of the pots would have a tendency to remove the spores 

 adherent to the grain, while in the case of diseased straw it would tend to 

 be absorbed, and leave the spores undisturbed. 



Infection of Wheat and Rye. 



The Flag smut was first found on wheat in Australia and was determined 

 by Wolff in 187-3 as being the same as that so abundant on rye elsewhere, and 

 named Urocystis occulta. Then Koernicke in 1877 considered the form on 

 wheat to be a new species, basing his determmation on morphological charac- 

 ters alone, and named it Urocystis tritici. If the same species of smut occurred 

 on both plants, then they ought to be mutually infective, the spores from 

 rye infecting the wheat, and the spores from wheat infecting the rye, and 

 infection experiments alone could settle it. 



The first experiment was carried out in pots containing ordinary garden 

 soil, and wheat and rye were cross-infected. There were six pots, and wheat 

 and rye were sown in them on 11th October, 1907. The ordinary seed of wheat 

 and rye was used as a check. Then seed wheat infected with the spores of 

 Flag smut from wheat collected on 28th September, and another lot with 

 those from rye collect3d on 21st July. Finally rye seed was infected with the 

 spores of Rye smut, and another portion with those from wheat. 



The first outbreak was in the rye infected with Rye smut, -40 days after 

 sowing, and about a week afterwards the wheat infected with the Flag smut 

 of wheat showed the disease. The rye germinated about two days before the 

 wheat. Although several plants germinated, only one each of rye and wheat 

 showed distinct traces of the disease, and they were each infected with their 

 own particular smut. These pot experiments are very useful for giving in- 

 dications of what may happen in the field, and they often show what to avoid, 

 as well as what to follow, upon a large scale. Another experiment was planned, 

 conducted in my own garden, in which there were six plots, with 20 grains 

 each, but otherwise similar to the first ; the same smut of wheat and rye being 

 used for infection as before. They were sown on 23rd May, 11)08, and on the 

 28th October three wheat plants out of twenty were found badly infected 

 with Flag smut, the infection having been brought about bv the spores of 

 wheat Flag smut. 



The plots were finally examined at the end of the year, but there was no 

 further development of disease. Although in these experiments there was 

 no disease in the rye, it was not owing to the spores being non-germinable, 

 for when placed on a slide in tap water and kept under a bell-jar thev ger- 

 minated freely in three days. On 12th August, 11)08, I duplicated the'plots, 

 in order to see what effect very late sowing might have upon the result. The 

 same smut of wheat and rye was used for infection. The late-sown rye grew 

 much bettor than the late-sown wheat, the latter in fact, turning out a com- 

 parative failure. In this experiment two plants of rye were found on (Hh 

 January, 1901). to be badly infected with their own smut, but none appeared 

 in the wheat plots, neither fr^m infection with Flag smut of wheat nor with 

 Ryfe smut. 



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