THIELAVIOPSIS PARADOXA. 



557 



i.e., a solution which contains the molecular weight in grams 

 in a litre : — 



In most of the recorded investigations into the action of 

 toxic substances on fungus spores, the concentration required 

 to prevent germination is all that has been determined. But 

 it is clear from the foregoing records, e.g., with tannic acid, 

 carbolic acid, and copper sulphate, that the spores are not 

 killed by much higher percentages of the toxic substance 

 than are required merely to inliibit germination. Further, 

 it is evident that the spores, when placed in a nutrient solution 

 which contains a toxic substance in excess of the inhibiting 

 percentage, do not germinate and die, as is frequently 

 supposed : they merely remain dormant. Whether they 

 ultimately die depends on the percentage of the fungicide 

 and the dm*ation of immersion. 



These points are of considerable importance in regard to the 

 action of fungicides on fungus spores. Determinations based 

 only on the non-germination of the spores give scarcely any 

 information as to the actual fungicidal value of the fungicide. 

 Copper sulphate, for example, in a concentration of 0-07 

 per cent., prevents the germination of Thielaviopsis, but, as 



6(11)10 



(72) 



