148 Wormald . — ‘ Brown Rot ' Diseases of Fruit Trees . 11. 
generally used as a useful nutrient substrate for agar cultures, were unob- 
tainable at the time the experiments were started, but dried peaches were 
available and these gave good results. 
Two grammes of the dried fruit were weighed out for every 100 c.c. of 
the liquid required, cut up into small pieces, and extracted with 100 c.c. of 
distilled water in a steam sterilizer at ioo° C. for one hour. The extract 
was filtered and transferred to test-tubes, 20 c.c. to each, which were 
then plugged with cotton-wool and sterilized by heating at ioo° C. for 
20 minutes on each of three successive days. The Petri dishes were 
sterilized by dry heat at i6o°C. for one hour. When cultures were to be 
started the contents of the tubes were emptied, with the usual precautions 
to avoid contamination, into the respective dishes ; these were inoculated by 
transferring to each a small portion of the mycelium from the edge of 
a vigorously growing agar culture. The dishes were then placed in a 
thermostat at 25 0 C. Thus the conditions under which the cultures were 
grown were the same for all the experiments, and a comparison could be 
made of the behaviour of strains cultivated at different times. Each 
experiment consisted of the culture and subsequent testing for oxidase of 
from 4 to 7 strains, both apple and Primus strains being included in every 
experiment. After 7 days’ growth the liquid contents of each plate were 
poured off into wide test-tubes, from which the liquid was withdrawn as 
required for the oxidase tests. 
Reynolds Green ( 11 ) says, in reference to the guaiacum test, ‘ most 
investigators do not find it give entirely satisfactory results ’. Woods ( 26 ), 
however, states ‘ that with proper care it is the best reagent which we have ’ 
for the detection of oxidizing enzymes. It has been used throughout this 
series of experiments, but, with the exception of No. 1, the results have 
always been checked and confirmed by testing simultaneously for the 
reaction with pyrogallic acid. The guaiacum emulsion was prepared by 
soaking 10 grm. of gum guaiacum in 100 c.c. of 95 per cent, alcohol, with 
occasional shaking, for several days before using ; 5 c.c. of this tincture were 
shaken up with 95 c.c. distilled water to make too c.c. of the white emulsion, 
which was prepared fresh for each experiment. The pyrogallic acid was 
used as a 2 per cent, solution prepared immediately before use. 
The following details of Expt. 6 (see table on page 151) of this series 
will serve as an example of the method adopted in applying the tests. 
Experiment 6. 
Four strains were used in this experiment : 
A. From an apple spur. 
B. From an apple canker. 
C. From a mummied cherry. 
D. Strain from Oregon. 
