520 



Journal of Agricultural Research 



Vol. nx. 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 o.i to 0.5 c. c. of the water by means of 

 a graduated i c. c. pipette into each Petri dish. In this way only 4 to 

 5 c. c. of the total water returned to the laboratory v/ere used in each 



Fig. 3. — Map showing the location of water spore-trap stations Nos. I to VT. Stations I and II are in the 

 chestnut coppice, the detailed composition of which is shown in figure -i ; 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 obser^'ation 

 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 



