Worm aid. — ‘ Brown Rot ’ Diseases of Fruit Trees . If. 155 
enzyme might be secreted when the fungus is invading the tissues of apple 
spurs. Experiments were therefore carried out with the object of determin- 
ing whether that or a similar enzyme could be detected in infected spurs. 
Experiment i. 
In this preliminary experiment a dead spur showing typical blossom 
wilt was obtained from a Lord Derby apple tree in the College plantation ; 
the current year’s growth (which was not yet fully lignified and therefore 
softer than the woody portion of the previous year) was cut off and the dead 
leaves and flowers removed. This short shoot, about 1-5 cm. in length, was 
pounded with about 1 c c. of water and ground in a mortar to a paste, which 
was washed out with a little more water into a test-tube and finally made 
up to 5 c.c. This extract was allowed to stand for a few minutes until the 
grosser particles sank to the bottom ; the liquid above was then poured off 
and 1 c.c. of it was transferred by means of a pipette to each of three test- 
tubes. One tube was heated in a water-bath at boiling-point for two 
minutes and cooled ; then to each of the three tubes were added 5 c.c. of 
guaiacum emulsion and the tubes were placed in an incubator at 25 0 C. 
Tubes 1 and 2 (unheated) gradually assumed a bluish tint, and after three 
hours were a pale blue ; in the third tube no change occurred. It appeared 
evident that an oxidase could be extracted from an infected spur, so other 
experiments were carried out to ascertain whether this enzyme was similar 
in action to that secreted by the fungus when growing in liquid culture 
media, and also whether it occurred exclusively in infected spurs. 
Experiment 2. 
An extract was obtained from another infected spur as in Expt. 1 and 
a normal (living) spur was also extracted for comparison. Three tubes of 
each extract were prepared as in the previous experiment, one of the three 
being heated before adding the guaiacum emulsion, and all were placed in 
the thermostat. 
The emulsion rapidly became coloured in the tubes containing the 
extract of the living spur, but the colour was much greener than in those 
tubes containing the infected material ; the latter were coloured more 
slowly, but eventually were approximately of the same tone as that obtained 
when using the liquid from pure cultures. 
The contrast between the two sets of tubes was very marked after 24 
hours : 
Extract of infected spur (unheated) and guaiacum emulsion : bright 
blue (approx. ‘ Russian Blue ’ of Ridgway’s scheme). 
Extract of normal spur (unheated) and guaiacum emulsion : bright 
green (approx. ‘ Deep Grape Green ’). 
Both tubes containing the heated extract remained unchanged. 
