400 Bulletin 167 



but indicate that when these two groups of organisms are asso- 

 ciated in the same sample of sap the fluorescent bacteria are 

 likely to gain the ascendency. The appearance of the samples 

 and the results of the plates indicated that the development of 

 the fluorescent group was stimulated by the presence of yeasts 

 and molds, with which they must compete. This may account 

 for the considerable number of failures which resulted from 

 attempts to inoculate unsterilized sap with cultures of yeasts and 

 molds. The average figures for the composite samples follow : 

 Color j.j, flavor 3, and score 663 ; the average depreciation from 

 control, color 3.3, flavor 1.5, and score 213. 



In eight cases, attempts at infection failed or at least the 

 introduced organism was not recovered. In a majority of these 

 samples the fluorescent bacteria appeared sooner or later and 

 exercised an influence upon the quality of the sirup. The average 

 color was 7, flavor 2.3, and score JJ2 ; average depreciation from 

 control, color 3.4, flavor 0.3. and score 103. 



Three sirups were made from natural sour sap, that is to say. 

 sap which was allowed to remain in the buckets late in the season 

 until it had seriously depreciated. One object of this procedure 

 was to determine what proportion of invert sugar might be ex- 

 pected in such material. Difficulty is often experienced in graining 

 sugar made from the last run sirups. This trouble probably 

 results from a large proportion of invert sugar, which of course 

 might be formed in the sap by the action of micro-organisms. In 

 the three sirups here reported, however, the proportion of invert 

 sugar was low. Two other samples of similar material yielded 

 sugar which grained readily The average figures for the three 

 sirups follow: color 20+, flavor 3 1 , and score 333; average de- 

 preciation calculated on first run control, color 16-}-, flavor I 1 , 

 and score 542. 



Thirteen samples were reserved for incubator controls. These 

 were treated in different ways in different series. Some of them 

 were so handled that they were only slightly inferior to the true 

 control, while in other instances they were very nearly comparable 

 to inoculated material. The greater part of the depreciation in 



