62 BACTERIA IN RELATION TO PLANT DISEASES. 



evidence of growth at the surface ; in a few there was a distinct yellow rim and pellicle (six- 

 teenth day). Old litmus-milk cultures (7 months) were dried down to about one-eighth of 

 the original volume : The liquid was then thick, syrupy, or gelatinous, and very dark-colored. 

 There were no tyrosin crystals, not even in very old cultures. According to Greig Smith, 

 milk cultures give a neutral reaction and the fluid remains unaltered. I attribute this state- 

 ment to incomplete observations, i. e., of first stages only of growth in milk. 



In Uschinsky's solution there is sometimes a feeble clouding, sometimes none at all. 

 Out of six attempts to grow the organism in this medium three failed utterly, although the 

 transfers were made from cultures known to be alive and the inoculations were copious. 

 The following is a note on two sets which did cloud : 



Tubes of Uschinsky's solution, inoculated from young agar streaks, were feebly clouded at end of 

 the first day, and thinly clouded at end of the seventh day with a scanty yellowish precipitate, and 

 without rim, pellicle, or pseudozoogloeae. These tubes were followed for 16 days longer, but there was 

 little change. The organism did not grow well in this medium (stock 982). In another set of six 

 tubes (stock 738) inoculated each with a 3 mm. loop from bouillon cultures 2 days old, all were clear 

 on the sixteenth day. On the thirty-ninth day two were clouded with a small amount of Naples 

 yellow precipitate. Twelve days later the other four tubes clouded. 



To test the action of the organism on cane-sugar, cultures were made in water contain- 

 ing Witte's peptone and i per cent cane-sugar (stock 809). The fluid became uniformly 

 thinly clouded (penholder barely seen behind four tubes, each 16 mm. in diameter). A 

 yellowish-white rim and a pale yellow precipitate appeared. On the twenty-second day the 

 cultures were tested with Soxhlet's solution. There was a distinct reduction of the copper 

 sulphate on boiling half a minute. 5 c.c. of the alkaline fluid and 5 c.c. of the solution of 

 copper sulphate in 50 c.c. of distilled water were used in each case, the fluid brought to a boil 

 in a clean porcelain capsule, and then the cultures added. It required about 15 c.c. of the 

 cloudy culture-fluid to reduce all the copper in 5 c.c. of the copper sulphate solution, boiling 

 2 minutes. There was a reducing substance in the cultures, and it is reasonably certain to 

 have come from the breaking-up of the cane-sugar into simpler sugars. The uninoculated 

 stock was tested as a check, but there was no such reaction : The fluid became and remained 

 a hyacinth blue. Previous to this an old cane-juice gelatin culture (stock 751) had been 

 tested in a similar manner, but there was very little reaction while the uninoculated cane 

 stock showed an abundance of reducing sugar in it on boiling 2 minutes with Soxhlet's solu- 

 tion. There was more reduction in the two uninoculated cane-juice gelatins (750 and 751) 

 than in the 4-months-old culture tested. This probably means that the reduced sugars had 

 been consumed as food. 



Greig Smith on the contrary says that the organism does not secrete invertase. In his 

 experiment saccharose-agar cultures were melted, dissolved in water, and treated with basic 

 lead acetate, etc. (Linn. Soc. Proc., 1902, p. 44.) Only 3 per cent of the saccharose had 

 been inverted to fruit-sugar, a quantity which he thinks the hydrolytic action of the small 

 amount of acid in the medium might easily have produced. Cobb is also of the opinion that 

 the organism does not act to any appreciable extent on cane-sugar. To determine the 

 action of Bacterium vascularum on cane-sugar he put 457 mg. of the air-dried gum obtained 

 from diseased canes with i gram of pure cane-sugar into 10 c.c. of water and allowed it to 

 stand 3 days. The solution was then tested. It was exactly like the check-tube, i. e., there 

 was no reduction of the amount of cane-sugar present. The experiment was repeated with 

 the same result. From these two experiments the conclusion is drawn that Bacterium vas- 

 cularum does not act to any appreciable extent on cane-sugar. To the writer this does not 

 appear to be a necessary conclusion. It is too broad an inference since (i) cane-sugar may 

 perhaps be reduced only when the organism is alive and growing; (2) the organisms in the 

 carefully dried gum may have been killed by light or by dry air in the process of drying ; (3) 

 the organism, although alive when put into the sugar solution, may not have found in it the 



