338 Bulletin 167 



tup; number oe micro-organisms in maple SAr 

 During the first two seasons covered by these studies (1907- 

 and 1908) no attempt was made to determine the bacterial count 

 in maple sap of different types. Attention was rather directed 

 to determining the predominating forms of micro-organisms 

 present, and to securing cultures to be employed as a basis for 

 the morphological and biochemical studies and for inoculation 

 work, which have constituted the major portion of the problem. 

 In connection with the field studies of the past three years, how- 

 over, some attention has been given to collecting data on the 

 number as well as the character of the micro-organisms present. 

 The time devoted to this feature of the work was limited and 

 the data secured is consequently more or less fragmentary, but 

 it appears of sufficient importance to warrant presentation. The 

 material examined was secured from several sugar places and 

 at various intervals during the season. 



For the purpose of enumeration the ordinary poured plate 

 method with dilutions was employed. Two types of media were 

 used. The first was ordinary nutrient agar ; the other, a synthetic 

 agar, less well adapted to the cultivation of bacteria than is the 

 ordinary agar but suited to the development of yeasts and molds. 



It had the following composition : 



Water 1000 parts 



Dextrose 100. 



Peptone 20. 



Ammonium nitrate 2.5 



Magnesium sulphate 5. 



Potassium nitrate 2.5 



Potassium phosphate 2.5 



Calcium chlorid 0.1 



Agar 15.0 " 



It should be understood that the figures given in the tables 



immediately succeeding are only approximate and that in most 



cases they are probably below the maximum because of the fact 



that the dilutions employed were usually insufficient to prevent 



serious crowding on the plates. The blank spaces in the column 



headed "synthetic agar'' may be taken as an indication that the 



sap in question was plated only on nutrient agar. 



