452 Scientific Proceedings^ Royal Dublin Society. 



found possible to reproduce conditions in microscopical preparations under 

 which the conidia remained viable and capable of infecting tubers for several 

 weeks. As these conditions resemble in many respects those which occur in 

 soil, it is reasonable to suppose that the explanations which will be given of 

 the phenomena observed in the preparations are also applicable to natural 

 conditions. 



This portion of the work also resulted in extending our knowledge of the 

 morphology and biology of the fungus in some important particulars, one of 

 which at least has a bearing on the fate of conidia in the soil. 



The findings of Hecke and Melhiis were first compared. Tor this purpose 

 the germination of conidia was tested in the following liquids, which were 

 sterilized before using: — (1) distilled water, (2) tap water, (3) soil extract, 

 prepared by the slow filtration of tap water through four inches of soil, and 

 (4) a I'o per cent, solution of glucose in distilled water. To observe the 

 effect of temperature, one set of germination tests in these media was carried 

 out at room temperature (which during these trials never sank below 10° C. 

 at night, or rose above 15" C. during the day, with one exception, when 22° C. 

 was reached), while another set was carried out in a constant temperature 

 incubator at 22°-23° C. Both sets were kept in the dark. Conidia were 

 derived from Petri dish cultures on potato slices, which were infected from 

 pure cultures on oat agar. Every care was taken to use uniform material 

 from the same culture for both sets of tests. The germinations were carried 

 out under cover glasses (except in some special cases), and the slides were 

 kept in moist chambers to prevent drying. It is possible in this way to 

 keep the same preparation under observation for several weeks, and to. 

 change the liquid at will without materially disturbing the conidia. 



Comparison of the effects of nutrient solutions and temperature on germina- 

 tion. — Our work on the conditions (so far as they were tested) governing the 

 germination of the conidia agrees best with that of Marshall Ward (25). 

 These conditions were found to be very complicated, as would be expected 

 from the results of earlier investigations. The comparison of the effect of 

 the solution and of the temperature was repeated seven times without 

 achieving a constant result, as may be seen in Table IV. 



