454 Scientific Proceedings, Royal Dublin Society. 



The following conclusions from this experiment seem to be justified (see 

 Table IV) :— 



7'emperature of 10°-lb° C. 



1. At a temperature of 10°-15°C. the regular method of germination 

 is by means of zoospores. With good material the germination runs 

 from 50 to nearly 100 per cent. 



2. Generally speaking, the number of conidia producing germ tubes 

 at this temperature is small, but it may under certain conditions exceed 

 the number producing zoospores. 



3. The iniluence of nutrient solutions on the production of germ 

 tubes was not apparent in the case of the sugar solution used, but there 

 was, perhaps, somewhat more evidence for it in the case of soil extract. 

 A somewhat larger number of abortive (unescaped) zoospores was found 

 in the sugar and soil solutions than elsewhere. 



4. There is considerable evidence that the tendency to produce germ 

 tubes at a temperature of 10°-15°C. rests in the conidia themselves 

 (see test of 26. 2. 21 at 10°-15° C). 



TemperaUcre of 22°-23° G. 



1. At 22°-23° C. the regular method of germination is by means 

 of germ tubes. The germination seldom exceeds 60 per cent., and is 

 generally less. 



2. Ordinarily the production of zoospores is rare, but conidia with 

 undifferentiated contents but with the papilla gone, or with contents 

 extruded, or containing abortive zoospores, are frequent. 



3. On one occasion (test of 1. 3. 21 at 22°-23'' C.) the production of 

 zoospores largely replaced that of germ tubes, indicating either a pecu- 

 liarity on the part of the conidia then used, or that temperature does 

 not act directly on germination, but influences it through some factor 

 which it generally (but not always) calls into play. 



4. The influence of nutrient solutions was not marked, but soil 

 extract seemed to favour tube formation. 



The tests carried out at 22''-23° C. gave percentages of germination which 

 were uniformly much lower than those found at the lower temperature. It 

 was evident that the conidia were near the limits of their development. It 

 is believed that the results recorded have little, if any, bearing on the con- 

 ditions under which blight epidemics occur. 



Effect of age on the. mctliocl of germination. — Some conidia germinate by 

 means of germ tubes under conditions which cannot be explained by reference 



