W. F. Bewley and W. Buddin 15 



extent of the growth, which could be made by the various fungi in the 

 actual well waters, samples of water were obtained from six different 

 wells; the samples varying in the quantity of organic matter they con- 

 tained. Tubes were filled at the rate of 10 c.c. per tube, plugged, sterilised 

 and inoculated from the pure cultures of the fungi isolated from the 

 water samples. In every case an appreciable growth resulted within 20 

 days and within 40 days the growth was sufficiently strong to show that 

 the waters tested were moderately good media for the growth of the 

 pathogens. There was a striking relation between the rate of growth and 

 the amount of organic matter in the water; the rate of growth in the 

 clearer waters being slower than that in the impure waters. 



The purification of contaminated waters. 



The purification of contaminated waters may be attempted along 

 three main lines, namely filtration, sterilisation by heat or sterilisation 

 by chemicals. 



Filtration. 



The beneficial results obtained by this method are patent when one 

 considers the efficiency of the filter beds utilised in the preparation of 

 pure water for domestic purposes. To be efficient, such filters require 

 constant overhauling and must be of fairly large extent and thus the 

 utilisation of filter beds on any but the largest nurseries does not come 

 within the limits of practice. Certain means of roughly filtering con- 

 taminated waters have been attempted with beneficial results. In one 

 case the contaminated water was allowed to percolate through a tightly 

 packed sand and coke filter, some two feet in diameter and six feet in 

 length. The resulting water proved to be free from fungus spores for the 

 first three months during which the filter was in use. After 12 months' 

 use the efficiency of the filter was slightly reduced, but there was still a 

 great reduction in the number of fungi present in the water after filtration. 



Sterilisation by chemicals. 



In view of the desirability of obtaining results fairly rapidly, it was 

 only possible to attempt a rough determination of the toxic action of 

 various chemical compounds upon the vegetative and "summer" spore 

 forms of fungi selected owing to their comparatively great commercial 

 importance as disease producers. The type of fungus growth used in the 

 tests was as follow: 



Pieces of mycelium of Phytophthora cryptogea, in such quantities as 

 are easily picked from a culture by an ordinary platinum needle, Avere 



