546 FETCH : 



III.— EFFECT OF FUNGICIDES, &c., ON THE SPORES. 



The following experiments sprang from an attempt to 

 discover in how far the usual fungicides were effective in 

 preventing the germination of the spores of Thielaviopsis. 

 The first three or four of the substances experimented with 

 were recommended for use in combating the coconut stem 

 disease, and the experiments were conducted in order to 

 demonstrate that they had no fungicidal action. 



The spores were sown in flasks containing sugar cane extract, 

 to which various percentages of the fungicide or other sub- 

 stance under experiment had been added. Flasks of about 

 40 c. c. capacity were used, and 20 c. c. of sugar cane extract 

 containing 6 per cent, of sugar was placed in each. This was 

 made up to 25 c. c. by the addition of the solution of the 

 fungicide, together with the required quantity of water. The 

 percentage of sugar, except where otherwise stated, was, 

 therefore, 4-8. The experiments were usually conducted in 

 duplicate, sometimes in quadruplicate. ; j 



A rather small supply of flasks prolonged the experiments, 

 and made it impossible to use spores from the same culture 

 throughout ; but in all cases they were taken from cultures 

 six days old. Black, fully matm^e spores were therefore only 

 used. Incubators were not available; and, therefore, the 

 experiments were subject to a range of temperature of about 

 10° F. , from 71° F. to 81° F. The range of temperature during 

 a single experiment was less than this, at most 71-79° F., or 

 73-81° F. 



Owing to repeated absences, it was impossible to make 

 continuous observations on the progress of all the cultures. 

 In many instances only final results can be given. But in all 

 cases the cultures were left until there was no probability that 

 any more in the series would develop. The results, therefore, 

 give the concentration required to prevent the germination of 

 the most resistant spores, which after all is what is required 

 in estimating the value of a fungicide. It has been determined 

 by other investigators that fungus spores fi'om the same 

 source vary gieatly in their power of resistance ; and Stevens 

 (18) states that an occasional spore may germinate and grow 

 perfectly normally in a solution w-liich prevents hundreds of 



