Flai^ Sin lit of Wlicat. 95 



Brefeld'' also germinated the spores iu water, and considers the whorl at 

 the apex of the promyceliiini as branches, since they never become detached. 

 In a nutritive sokition it was the same, only the whorl of branches grew out 

 and branched more freely. These cylindrical bodies at the apex of the pro- 

 mycelium behave Uke conidia, by putting forth a longer or shorter germ-tube, 

 and there is no evident reason why they should not be regarded as such. 



The conidia are said to give off lateral germ-tubes, and Wolffs gives a 

 figure of one of the conidia producing a lateral germ-tube at its base. I have 

 examined thousands of germinating conidia, and while the germ-tubes grow- 

 ing out at the tip may curve laterally, or even backwards, none were produced 

 elsewhere than at the free end of the conidia. 



Duration of Germinating Power. 



These spores are well protected by their layer of sterile cells, and are well 

 adapted from their structure to retain their vitality for some time. How 

 long they retain their infective power, both in the soil and out of it, has not 

 yet been definitely settled. In considering measures for dealing with the 

 disease it is important to know how long this period lasts, for in a rotation of 

 crops which is the most likely means of coping with it, it is necessary to 

 know, if possible, how long the wheat crop has to be discontinued before it 

 will be safe to sow it again. Experiments are being conducted to settle this 

 point. A portion of a paddock, the soil of which is known to be badly infested 

 with the smut, has been fenced off, and wheat wall be continuously grown 

 in certain parts of it to see how long, under ordinary cultivation and conditions, 

 there is danger of infection, when every precaution is taken to prevent 

 re-infection. Already pot experiments have been carried out, in which it 

 was shown that seed dusted with spores from the crop immediately preceding 

 was infected, while seed dusted with spores from the crop previous to that 

 was not infected. But they are not sufficiently decisive and extensive 

 enough to allow definite conclusions to be drawn from them. 



Mode of Infection. 



Since the host-plant is generally destroyed by this smut before the 

 flowering stage is reached, infection through the flower is excluded, but 

 experiments were carried out to test if it occurred in the seedling stage or later 

 on. Seed wheat was obtained from a district in which this smut did not 

 occur, and planted in pots containing ordinary garden soil. There were 

 three pots — one used as a check in which the seed was uninfected, a second 

 in which the seed was dusted with plenty of spores, and a third in wliich 

 the spores were dusted over the plants when about 6 inches high. 

 The result was that the smut developed only where the seed was 

 dusted with spores, showing that it is probably the young seedling which 

 is attacked, and that there is no infection when the plant is above ground. 

 The experiment of dusting the seed with spores was re])eated with a similar 

 result, and when in another ex])eriment the young plants about 3 inches 

 high were also dusted with spores and kept moist by bein ;f covered with a 

 bell-jar, there was no infection. In another . experiment, affected straw 

 from the previous season's crop was added to the soil, and the clean grain 

 sown along with it. In about ten days after sowing the mycelium was 

 obtained in the young leaf, and in 40 days after sowing the first production 

 of new spores was observed. These conditions would be very similar to those 

 occurrhig in the field, only there the diseased straw would be more in patches 

 and not likely to be so generally distributed. In this experiment 18 plants 

 out of 35 were diseased, or a percentage of 51. 



