37 2 Wormald. — ‘ Broivn Rot ’ Diseases of Fruit Trees. 
glasses, held in forceps, are passed several times through a Bunsen flame; 
one is then inverted over the other and both allowed to cool, when into the 
lower is poured about i c.c. of sterilized distilled water. Particles of 
pulverulent pustules are brought in contact with the water, and the conidia, 
becoming detached, float on the surface. By means of a flamed platinum 
wire loop (i mm. diam.) drops are transferred from the watch-glass to the 
surface of sterilized nutrient agar in a Petri dish. As this operation is 
carried out in a room set apart for culture work it was found possible to 
examine these drops directly, the cover of the dish being removed, under 
a low power of the microscope with but little risk of contamination. Since 
the conidia float on water the surface of the drop is brought into focus and 
examined for the presence of floating conidia. Generally with one loopful 
three drops of water can be deposited on the agar without recharging the 
loop, and this is a convenient number to examine before evaporation causes 
their obliteration. When a drop is found to contain a single conidium the 
cover of the dish is replaced and a ring of ink is made on the bottom of 
the dish to mark its position. Several such marked drops having been 
obtained, the dish is placed in a drawer at room temperature until the 
following day. After twenty-four hours the inverted plate is examined under 
the microscope with a i-inch objective. One of the rings of ink is brought 
into the field and the microscope tube is gradually lowered until the agar is 
in focus as indicated by the appearance of numerous small granules; the 
layer of granules last seen before they disappear from view indicates the 
surface of the agar, and this is then examined at that level for the germi- 
nating conidium within the ring of ink, the blurred outline of which is still 
discernible. 
It will, in general, be seen at this stage whether the conidium is truly 
isolated or whether contamination has taken place. In most instances the 
length of the germ tube and its mode of growth were also noted, and it was 
generally found that the germ tube of M . fructigena could be distinguished 
from that of M. cinerea } 
On the second day after isolation they are again examined and two 
or three of those which are found to be uncontaminated, and quite isolated 
from other germinating conidia, are transferred to another agar plate. 
Usually this transference is made after forty-eight hours, but occasionally, 
when the temperature of the room was low and growth had not been 
vigorous, the sporelings were removed on the third day after the isolation 
of the conidia. When the resulting mycelial discs are 2-3 cm. in diameter 
(representing about eight days’ growth) small portions of the mycelium are 
removed from the periphery of the disc and placed on agar slants in test- 
tubes for future use, and when conidia are required sub-inoculations are 
also made on sterilized potato. 
1 Further details will be given in Part II of this papqr. 
