456 Scientific Proceedings, Royal Dublin Society. 



arrested germination. It soon became possible to distinguish between conidia 

 ■ which were incapable of development and those the development of which was 

 merely delayed. The least sign of plasmolysis is a sure index of death, but 

 before this appears a peculiar darkening and granulation of the protoplasm 

 indicate, according to our experience, that the conidium is incapable of 

 development. 



It was found that some slides (particularly those kept at 23° C.) became 

 badly contaminated with bacteria and yeasts, and that under such 

 conditions germination was confined to a zone about 4 mm. wide near the 

 edge of the cover glass. "Within this ring a negligible amount of germination, 

 or none whatever, was to be seen. If, however, the slide was very carefully 

 and repeatedly irrigated with its appropriate solution, the process being 

 watched under the microscope and extreme caution being exercised not to 

 disturb the conidia, it was found that the germination of a large number of 

 the central conidia could be brought about. 'J'hree hours after irrigation 

 the result was sometimes apparent, but sometimes it took twenty-four hours. 

 While traces of indirect germination have been seen under these circum- 

 stances, germ tubes are almost the invariable rule, irrespective of the tempera- 

 ture or of the nature of the solution. 



This experience was repeated many times, at first involuntarily and 

 afterwards of set purpose. A test in tap water at 23° C, begun on 2. 3. 21, 

 became contaminated with bacteria after twenty-four hours, and then showed 

 only 18 conidia with germ tubes out of 198 conidia examined. Most of these 

 were near the edge, there being very few in the centre. After irrigation and 

 a further period of twenty-four hours, the number of conidia with germ tubes 

 was 112 out of 271 examined. Another slide containing soil-extract and 

 belonging to the same series also became contaminated and showed four conidia 

 with germ tubes out of a large number examined after twenty-four hours. 

 On irrigation the number rose to 34 in 89. 



That it was the presence of bacteria which prevented germination was 

 proved repeatedly by setting irp some tests under practically sterile con- 

 ditions, while in others bacteria were introduced. The former (at 10°-15° C.) 

 showed numberless zoospores after about three hours, and after twenty-four 

 hours the majority of the conidia had germinated in this way all over the 

 slide. Where bacteria had been introduced perfect zoospore formation was 

 found only in a narrow zone near the edge of the cover glass, while there 

 might be attempts at zoospore production elsewhere. If now fresh water 

 were copiously introduced a great access of germination resulted in most 

 cases, germ tubes only being produced. Control slides to which no water was 

 added showed no change, or at most an entirely negligible amount of tube 



