122 
William Brown. 
Means of estimating and regulating the density of spore suspension 
were also devised. The following results are well attested. 
With any given lot of spores when sown on glass in pure water 
the percentage of germination is a function of the concentration of 
the spores, the higher the concentration of spores present the lower 
the relative and absolute amount of germination. Thus, with any 
particular lot the concentration can be increased so that germination 
is totally inhibited. 
When the spores are sown in very dilute nutrient a similar 
phenomenon is observed, the concentration required to produce 
inhibition of germination being increased. 
The percentage and vigour of germination of spores under a 
given set of circumstances depends also upon the nature of the 
spores. The main fact revealed in this connection is that age of 
spores diminishes capacity for germination. Thus the germination 
in water of spores from somewhat old cultures can be inhibited by 
a lower concentration of spores than is the case with spores from 
a young culture. This process might be described as one of 
“ attenuation ” by age. Other methods of attenuation can no doubt 
be devised—such as, perhaps, tbe maintainance of the spores under 
somewhat unfavourable physiological conditions. A thorough 
examination of these relationships is certain to be of great value in 
the elaboration of methods for the experimental treatment of the 
whole subject. 
A method was also sketched by which the amount and vigour 
of germination under any circumstances could be controlled by 
subjecting the spores to the influence of varying percentages of 
carbon dioxide in the atmosphere. It was found that the effect of 
small amounts of nutrient could be neutralised by placing the fungus 
in the appropriate concentration of carbon dioxide. Thus while 
germination of a particular sample in pure water could be inhibited 
by an atmosphere containing 10% carbon dioxide, a pressure of 30% 
carbon dioxide was necessary to inhibit germination in a certain 
concentration of turnip extract. 
The amount of germination in water can also be controlled by 
addition of very small amounts of alkaline carbonate. Evidence 
was also obtained that the effect of slight concentration could be 
neutralised by the addition of the requisite amount of neutral 
nutrient solution. The experimental possibilities of this method 
have not yet been investigated sufficiently fully to allow of further 
statement. 
