152 CROWN-GALL OF PLANTS. 



POPLAR. 



Tests in 1910 hy Doctor Smith. — On July 25 three transfers were 

 made from 3 subcultures to tubes of nitrate bouillon. The tests were 

 made on the eighth day when there was a nearly clear fluid, a white 

 pellicle covering the whole surface and not much precipitate, but 

 some flocks and strings on one side next wall of tube. Result : Check 

 and 3 cultures — all negative. Nitrate present in each tube. This 

 was the organism called Flats poplar. 



REMARKS. 



A few of these contradictory results are to be explained on the 

 hypothesis of contaminating organisms. When the blue color v/as 

 merely local and shook out readily, the phenomenon would seem to 

 be different in something more than degree from that ordinaril}^ 

 encountered. Wliether nitrate reductions by bacteria are all alike 

 and only a matter of degree, or whether there are two or more distinct 

 mechanisms of reduction, is still an open question. Possibly one 

 form is due to the direct action of sulphur compounds, while another 

 depends on the activity of some enzyme. 



The 1910 tests were made wdth 1 c. c. of opalescent boiled starch 

 water (distilled water and starch prepared from potato in the labora- 

 tory) ; 1 c. c. of 1 : 250 fresh potassium iodide water, and 6 drops of 

 1 : 2 c. p. sulphuric-acid water. The checlcs were tested, the reagents 

 were tested, and when results were negative the bouillon was also 

 tested to see if nitrate was actually present. Frequently litmus tests 

 were made and all of the cultures may be assumed to have been 

 alkaline to litmus. 



GROWTH IN BOUILLON OVER CHLOROFORM. 



Inoculations from a 14-day peptone bouillon culture, examinations 

 on the twenty-tliird day. All grew readily, except quince. Least 

 growth in case of beet, chestnut, and newest daisy. To each tube 

 containing 10 c. c. of -}- 15 peptonized beef bouillon was added 5 c. c. 

 of cliloroform. The tubes were not agitated. 



INVERSION OF CANE SUGAR. 



The organisms were grown for 16 days in filtered river water con- 

 taining 2 per cent Witte's peptone and 2 per cent c. p. cane sugar. 

 On boiling with Fehhng's solution (50 c. c. distilled water, 5 c. c. alka- 

 line solution, and 5 c. c. CuSO^ solution) the cultures fell into 3 

 groups as follows: 



(1) Negative: Check tubes, sugar beet, new chestnut. 



(2) Slight to moderate reduction. Apple hairy-root, new apple 

 (slight), peach, grape. 



213 



