Micro-organisms of Maple Sap 559 



and more yellow-green. In the old cultures the agar had as- 

 sumed a brownish to amber color. Fluorescence was not as 

 strongly evidenced by some strains as by others. The strongly 

 fluorescent strains were: Ps. fluorescens, CXLVIII, CXII, 

 CXLV, Ps. mesenterica, CXL, Ps. tenuis and LI named ap- 

 proximately in the order of their fluorescing powers. Ps. alba, 

 Ps. longa, Ps. putrida, and XXXVI showed moderate fluores- 

 cence. Strain CXY was at most doubtfully fluorescent. 



5. Gelatin stab at 20° C. — Gelatin media were prepared 

 with "Nelson's Photographic Gelatin No. 1," and a "Gold Label" 

 gelatin. Sometimes 10 and sometimes \ 2' < were employed. 

 Neither the percent of gelatin nor the brand was observed to 

 have any significant effect on the cultural characters. ( )n gela- 

 tin media there were two types among the 13 strains, a liquefying 

 and a non-liquefying type, the latter including two very tardy 

 Iiquefiers. However, a sharp division line between types does 

 not exist. 



Liquefying type. — To this group belong Ps. fluorescens, Ps. 

 mesenterica, CXII, CXV, CXLV, CXLVIII, and XXXVI. 



Ps. fluorescens. — In 18 hours a slight growth appeared as a 

 filiform whitish line. Crateriform liquefaction began in two days 

 gradually extending the shallow crater until the liquefaction 

 assumed a stratiform type. The fluid was at first yellowish white 

 and moderately turbid, the stab being filiform and finely villous 

 above, beaded and finely villous below. A slight green fluo- 

 rescence was apparent, but only in the liquid portions. The 

 fluorescence in gelatin, -\-io Fuller's scale, was never as marked 

 as in agar of the same reaction. The influence of the reaction 

 upon fluorescence is apparent from the results of two series of 

 gelatin cultures, one of which had an initial reaction of — 4.7 Ful- 

 ler's scale and the other of — 12. The fluorescence appeared 

 earlier and became noticeably more intense in the more alkaline 

 medium, showing that a slightly alkaline gelatin is more favora- 

 ble to the development of fluorescence than a neutral or acid one. 

 This is in accord with the statements of Thumm (31) and Tor- 



