55 



from the starch enough food for its normal growth, and I am surprised 

 that this explanation did not occur to me at once. The organism grows 

 fairly well until the small amount of grape sugar present in the potato 

 is exhausted, and thereafter, when thrown wholly upon its own 

 resources, makes only an extremely feeble growth, corresponding to 

 its very feeble diastasic powers. This conclusion rests upon the fol- 

 lowing experiments: 



Iodine Starch Reachton. 



My uninoculated potato cylinders when tested with iodine potas- 

 sium iodide diluted with water, or with iodine crystals dissolved in 

 absolute alcohol to saturation and then diluted with water as required 

 for use, always yielded an immediate bright blue reaction. The starch 

 reaction was also strong after the /^s. hyacintid had been grown on 

 them for several weeks, although there was always evidence of slight 

 diastasic action to be found in the purplish color assumed by some of 

 the grains. The following are transeripts from my notes. 



(1) Some fragments of potato scraped from immediately under the 

 yellow slime on a culture 30 days old were put into an old solution of 

 iodine-glycerine. They became black at once, and when crushed out 

 and examined under the microscope were brownish purple — i. e., more 

 brown purple than the starch from a check tube. Tested with alcohol- 

 iodine diluted with tifteen or twenty times its bulk of water, the starch 

 of the potato in the check tubes became pure blue. In the culture, 

 immediately under the yellow slime, most of the starch-bearing cells 

 became purple, but occasionally one was nearly pure blue. Cells deep 

 in the cylinder reacted blue. 



(2) On the thirty- first day another tube of the same lot was tested 

 with alcohol-iodine, diluted with thirty or forty times its bulk of 

 water. When this fluid was put on scrapings from a check tube, the 

 reaction was pure blue; when it was put on scrapings from imme- 

 diately under the yellow slime, the starch reaction was purple and blue 

 purple. 



(3) A year previous scrapings were made close under the bacterial 

 layer of a culture 30 days old and tested with iodine potassium iodide. 

 There was a strong blue-black reaction. Under the microscope, how- 

 ever, some of the cells were paler than others, indicating that some 

 of the starch grains had been acted upon slightly. 



(4) On the twenty-ninth day a potato cylinder, bearing a typical 

 growth of the yellow slime and uniformly grayed, w^as broken across 

 the middle and tested with iodine alcohol in water. The middle part 

 of the cylinder reacted l)lue. The outer pait, close under the bacte- 

 rial layer, gave either a reddish or purplish blue reaction. 



No potato cultures of this organism were ever tested which did not 

 give a very decided reaction with iodine. The importance of this fact 



