26 Germmafioii of Spores. 



grew out into slender elongated filaments, but no conidia were formed. In the 

 dark a few of the promycelia produced on^- or two conidia. In another experi- 

 ment, there was no germination after two hours, but in four hours occasional 

 spores in the light had produced promycelia about twice or thrice as long as 

 the spore, while in the dark only a very few had germinated, and the pro- 

 mycelia were much shorter, only about the length of the spore. At the end 

 of twenty-four hours the slides Avere again examined. In the dark only a 

 comparatively few of the spores had germinated. The promycelia varied in 

 length from .30 to 52 ^(, either without septa or 1-3 septate, and bearing some- 

 times one or two lateral and a terminal conidium. Only in rare cases was a 

 conidium produced at the end of another while still attached. In the light 

 there was luxuriant germination, and the great proportioji of the spores had 

 germinated. The characteristic feature was that the promycelia grew out 

 into long, slender, often wavy filaments, which readily became detached, 

 reaching a length of 200 -.300//. Only rarely were conidia formed, and some- 

 times two promycelia proceeded from the same spore. 



I have only tested the effect of light and darkness on the oi\e species of 

 spore, but Fischer von Waldheim^ also found that the germination of smut 

 spores was retarded by withholding the light — that light had a stimulating effect 

 o]i germination. In Ustilago carbo ( = Ustilago avence) it delayed the ger- 

 mination for several hours, and also caused the promycelium to be frequently 

 bent in a knee shape. 



Effect of Exposure to Sunshixe on Germination. 



It is a common belief among farmers that long exposure to the sun's rays 

 in summer kills the bunt spores, and they account for the general absence of 

 bunt in self-sown wheat by the spores on the exposed grain being destroyed 

 in this way. Laurent^ was induced to investigate the subject by observing 

 that in some districts a burning sun at the time of sowing the wheat diminished 

 the chances of infection. He took bunt spores and exposed them to the full 

 sunlight in a glass vessel, and at the same time he exposed other spores to the 

 same light passed through a layer of a solution of sulphate of cjuinine three 

 centimeters thick. The temperature of the surrounding air did not rise above 

 40° C. After eight hours it was found that the spores fully exposed to the 

 sunlight did not germinate at all, even in a nutrient solution of unfermented 

 beer, while the spores shaded entirely from the sun germinated freely. The 

 spores which were shaded from the chemical rays of the sun by the solution 

 of sulphate of quinine did not lose their germinating power, even after sixteen 

 hours of exposure to a very hot sun. so that it may be assumed that while 

 the exterior spores of a bunt-ball are killed under these conditions, the interior 

 spores are still capable of germination. 



Farrer^ also carried out experiments to test the effect of dry heat on bunt 

 spores, and since it was believed that soaking the seed wheat in water for a 

 quarter of an hour at 57° C. had the effect of killing the spores, he tried this 

 heat in the dry state, as well as higher temperatures for the same time. The 

 result was that the higher the temperature the smaller was the proportion of 

 seeds which produced plants, and the greater the proportion of plants which 

 were bunty. At 54° C. of dry heat about 2 • 6 per cent, of the infected grains 

 lost their germinating power and 3 per cent, were bimty, while at 104° C. 

 three out of 136 seeds grew, but none formed ears. The direct heat of the sun 

 may have a different effect on spores than dry heat, yet Farrer^ says : — " My 

 experiment with dry bunt shows conclusively. I think, that it is not the heat 

 of the sun which kills the spores of bunt which are left on the ground: it is. I 

 think, moisture — the moisture from lains and dews, the moisture which comes 



