158 Wormald. — ‘ Brown Rot * Diseases of Fruit Trees. II. 
Result : 
Extract of infected spur. Extract of normal spur. 
Unheated. Heated. Unheated. Heated. 
4 hrs. no change no change deep yellow no change 
24 hrs. ditto ditto ditto very pale yellow 
The result was confirmed in three other similar experiments. The 
freshly made extracts, after being centrifugalized, were in each case almost 
colourless, but with slight turbidity. 
Experiment ii. 
In this experiment the action of the enzyme in an infected spur on the 
chromogenic substance of the normal spur was examined. A normal spur 
was extracted with 10 c.c. distilled water ; this extract was centrifugalized and 
then heated in a water-bath for 5 minutes. Two tubes were set up as 
follows : 
(1) 5 c.c. of this extract + 1 c.c. of unheated extract of an infected spur. 
(2) 5 c.c. of this extract + 1 c.c. of heated extract of an infected spur. 
The tubes were incubated at 25 0 C. At the end of 8 hours the 
contents of both tubes were distinctly yellow, but the liquid in (1) was of 
a deeper colour than that of (2). 
The experiment was duplicated, using two other spurs, and a similar 
result was obtained. 
It would seem, then, that an extract of a normal spur contains a sub- 
stance which darkens in colour on contact with air, but that the process is 
hastened by the enzyme (found in infected spurs) secreted by the fungus. 
The results of these experiments lead to the following conclusions : 
(1) That in the extract of a normal (healthy) flowering spur of apple 
trees there is present some substance, probably a tannin, which assumes 
a deep yellow colour when the extract remains in contact with the air. 
That this colour change is in part due to enzyme action is suggested by the 
fact that the action is retarded when the extract has been previously 
heated, but such an enzyme, if present, gives no reaction with guaiacum. 
In addition there is evidence that flowering spurs also contain an oxidase 
(reacting with guaiacum) at about the time the flowers are setting into fruit, 
but that later it cannot be detected. 
(2) That in an infected spur there is present an enzyme which reacts 
with guaiacum and oxidizes pyrogallic acid. 
(3) That the chromogenic tannic substance present in a spur is oxidized, 
on infection, by the enzyme secreted by the fungus, so that the centrifugalized 
extract of the infected spur no longer contains the tannin, which must 
therefore have been either assimilated by the fungus or deposited in the 
tissues in an insoluble form. 
Thus that form of Monilia cinerea (referred to in this paper as forma 
