36 Infection. 



favorable for germiiiatiou, and when placed on the young seedling in dihite 

 nutritive solution, they germinated without loss of time and directly produced 

 infection. 



In the case of stinking smut of wheat, there is no difficulty in securing 

 well preserved material. The unbroken smut-balls are filled with the un- 

 contaminated spores and require only to be crushed in order to dust the grain 

 to be infected. 



The Influence of Temperature on Infection. 



Brefeld* came to the conclusion, as the result of experiments with oat 

 smut, that a low temperature at the time of germination favours successful 

 infection, so that sowing in the spring, when a higher temperature than in 

 winter usually prevails, is less favorable to it. But Tubeuf- and others proved 

 quite the contrary, that a high temperature brought about a higher degree of 

 infection, and they recommend late autumn sowing as a means of reducing 

 the amount of smut. 



On the other hand, it has been proved by carefully conducted experiments, 

 that in the case of stinking smut of wheat, sowing late in the autumn, when 

 the temperature is low, encouraged it, other things being equal. In all these 

 experiments, however, it must be borne in mind, that neither temperature 

 nor infection ought to be considered independently, but that there are modi- 

 fying factors which must be taken into account. Thus rapidity of germina- 

 tion and a quick growth, will counteract the effects of temperature, for if the 

 fungus cannot keep up with the rapidly elongating plant and reach the growing 

 point, the host-plant will remain sound, in spite of the temperature. 



Hecke' has considered the influence of temperature in its threefold aspect 

 of — 1st. Effect upon the germination of the spores and the seed grain ; 2nd. 

 Upon the duration of the infective stage of the host-plant ; and 3rd. Upon 

 the possibility of the fungus reaching the growing point of the host-plant. 



1. If the temperature of germination be compared for the fungus and 

 its host, it is found that in wheat the minimum is practically the same for 

 both. For the wheat it is 3-4.5° C, and for the spores of stinking smut, 5° C, 

 so that, usually, the wheat and the spores will germinate together. But in 

 the case of oats, there is a considerable difference. The minimum tempera- 

 ture for the germination of oats is 4-5° C, while the spores require 5-11° C, 

 hence the oat itself may germinate at a low temperature while the spores 

 remain stationary. 



2. Cold and damp weather tend to retard growth, so that the infective 

 stage is prolonged, and at the same time, the tissues being soft and tender, 

 infection is rendered more certain. 



In the stinking smut of wheat, the principal effect of a low temperature 

 consists in lengthening the period during which infection is possible, for the 

 spores and the wheat, germinating together, along with the retarded growth, 

 will insure the fungus filaments inside the plant reaching the growing point. 



3. Since our Avheats are all sown in the autumn or early winter, there is 

 little rapid growth at first as a rule, so that the fungus has sufficient time to 

 reach the growing point and estabhsh itself in the host-plant. But it is in 

 the summer wheats that the influence of temperature is most marked in favour- 

 ing or hindering the fungus in reaching the growing point, and this may ac- 

 count for the great variety in susceptibility shown by such wheats towards 

 the stinking smut. 



It will now be clearly understood why a low temperature at the time of 

 sowing, especially if the soil is damp, will be favorable to the infection of 

 wheat by stinking smut, while in the case of oat smut it will be rather the re- 

 verse, since it retards the germination of the spores. 



