520 Journal of Agricultural Research Vol. ILL, No. 6 
METHOD OF MAKING A TEST 
At the end of an exposure period the contents of each dish were emptied 
into sterile flasks provided for the purpose and transported to the labo- 
ratory at the University of Pennsylvania, where the work of making an 
analysis was completed. They were then replaced with other sterile 
dishes and sterile water introduced as before. 
For each water spore trap 15 to 20 plate cultures were employed, and 
these were made by introducing 0.1 to 0.5 c. c. of the water by means of 
a graduated 1 c. c. pipette into each Petri dish. In this way only 4 to 
5 ¢. c. of the total water returned to the laboratory were used in each 
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EXPLANATION \\ = a “a 
Location ofa re WA \ ee A 
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FIG. 3.—Map showing the location of water spore-trap stations Nos. Ito VI. Stations I and II are in the 
chestnut coppice, the detailed composition of which is shown in figure 1; Stations III to V are at various 
distances from the same coppice; Station VI is to the north of a mixed chestnut and oak woodland. 
test, but special pains were taken to secure a uniform suspension before 
the removal of the quantities used. Chestnut-bark agar was used for 
all of these analyses (see p. 496 for formula) since experience had proved 
that it was a poor medium for the growth of bacteria, which were always 
present in some quantity. In fact, the medium is so unfavorable for the 
development of ordinary bacteria that in most cases the colonies remained 
as minute specks during the period the plates were under observation 
and with proper dilution offered no hindrance to the development of 
colonies of Endothia parasitica and other fungi. All cultures were incu- 
bated as nearly as possible at 25° C., and the colonies of fungi suspected 
of being the chestnut-blight fungus were marked at the end of three days. 
The count was completed on the fifth day, and any uncertain colonies 
