40 



[Vol. 10 



GARDEN 



communis, B. vulgaris, and a species of yeast isolated from a 

 compressed yeast cake. 



The basic culture solution used throughout was a Dunham's so- 

 lution to which 1 per cent of the following test substances 

 (Merck's, except starch) was added: (1) glucose (H. P.), (2) 

 fructose (cr.), (3) galactose (powder), (4) saccharose (H.P.) 

 (5) lactose (H. P. cr.), (6) maltose (powder), (7) dextrin (H p' 

 powder), and (8) potato starch (Heil's). 



The nutrient solutions used were not adjusted by the addition 

 of acid or alkali. As a matter of fact, it was determined in a 

 preliminary experiment that if small amounts of acid (HC1) 

 were added to adjust the reaction a considerable hydrolysis of 

 certain disaccharide sugars resulted during the process of steril- 

 ization, regardless of whether the latter was accomplished in the 

 autoclave or in the Arnold sterilizer (table ix). The Dun- 

 ham's solution employed as a basis of the nutrient solutions used 

 was found to be P„ 7.0, approximately. The P H of the several 

 sugar broths employed was not determined, but it is unlikely 

 that they differed markedly in H-ion concentration from the 

 Dunham's solution. 



Invigorated cultures of the several microorganisms at hand 

 were employed. Ten-cc. volumes of the media were measured 

 into special culture tubes, called wasp tubes (see pi. 2, fig. 5). 

 (The wasp tube was suggested to me by Dr. G. W. Freiberg, for- 

 merly of this laboratory, and has greatly facilitated and expe- 

 dited my work.) These were plugged in the usual manner and 

 sterilization was accomplished in the autoclave (see table ix). 

 Duplicate cultures were made, and a number of controls were 

 carried along with each series of cultures. All cultures were incu- 

 bated at 28° C. for 6 days, as it was found that there was no point 



in carrying the cultures for a longer period. Chambers ('20) 

 has recently contributed a convincing explanation of why evi- 

 dences of the metabolic activities fail after a few days in certain 

 sugar-broth cultures. 



Shaffer's (14) method for the quantitative estimation of re- 

 ducing sugars was used with slight modifications. This develop- 

 ment of the permanganate titration method of Bertrand is of 

 special value to workers in plant physiology because it enables 

 one quickly and accurately to determine the amount of sugar 

 as low as 2 mgms. The copper-reducing value of the culture 



