BLACK ROT OF CRUCIFEROUS PLANTS. 



325 



mineral solution with cane-sugar and ammonium chloride as the nitrogen food. It grew 

 feebly in these media when glycerin was substituted for the sugars, and not at all in the 

 potassium nitrate solution when glycerin was substituted for cane-sugar. 



These statements are perhaps open to criticism owing to the difficulty of obtaining 

 cane-sugar and mineral salts entirely free from organic nitrogen. If in the presence of air 

 this organism can use glycerin as a carbon food and if it can take nitrogen from potassium 

 nitrate it is difficult to understand why it did not grow when glycerin 

 was substituted for the cane-sugar. Brenner offers no explanation. 

 The writer's interpretation is that the organism obtained its nitrogen 

 not from the potassium nitrate, as Brenner supposed, but from some 

 unsuspected, slight impurity in his cane-sugar and consequently when 

 glycerin was substituted growth could not take place because there 

 was no available nitrogen food. A further reason for this conclusion 

 is that I have repeated Brenner's experiments, using chemicals sup- 

 posed to be pure, but certainly not entirely free from extraneous sub- 

 stances, and have obtained somewhat contradictory results. More- 

 over, a very slight, but distinct growth was obtained in twice distilled 

 water, to which only the mineral elements of Fischer's solution had 

 been added, to wit: Dipotassium phosphate, magnesium sulphate, 

 and calcium chloride. A decidedly better growth was obtained by 

 adding cane-sugar, but this growth was not increased or only slightly 

 increased by the further addition of potassium nitrate. The incom- 

 plete culture medium (supposed to be free from nitrogen but probably 

 not altogether free) gave as good results, or nearly as good (clouding 

 and bacterial precipitate), as the one made complete by the addition 

 of potassium nitrate. A third objection lies in the fact that the or- 

 ganism does not reduce nitrates to nitrites or to nitrogen, so far as can 

 be determined by the starch-iodin sulphuric acid test. 



This experiment was repeated again in 1909 using for the potas- 

 sium nitrate Merck's guaranteed reagent, with the following results: 



Notes of July 30, 1909, on inoculations of June 29, which were by 2 

 mm. loops from young bouillon-cultures into 10 cc. portions in very clean 

 test-tubes of resistant glass. 



(1) Fischer's mineral solution consisting of distilled water, dipotassium 

 phosphate, magnesium sulphate and calcium chloride. 



Fluid cleared, slight yellow precipitate. Earlier, i. e., during 

 the first 2 or 3 weeks, there was a feeble clouding showing presence 

 of N. and C. in the medium. 



(2) Fischer's mineral solution plus ordinary white cane-sugar. 



Fluid nearly cleared. A very slight distinctly yellow precipi- 

 tate same as No. 1 . Earlier the fluid was feebly clouded. 



(3) Fischer's mineral solution plus c. p. cane-sugar. 



Fluid cleared. Slight yellow precipitate. Closely like 1 and 2. 

 During the first weeks there was the same amount of very thin 

 clouding. The change in sugar made no change in the behavior. 



(4) The same as No. 2 plus 1 per cent KNCh, (Merck's G. R.). 



Thinly clouded, some pseudozoogloea?. A small amount of yellow precipitate, 

 tinctly more growths than in Nos. 1, 2, or 3. 



(5) The same as No. 3 plus 1 per cent KNO, (Merck's G. R.). 



Like No. 4 in clouding, etc. There is a scanty precipitate without much yellow in it. 

 More growth than in Nos. 1 to 3. 



Fig. 129.' 



Dis- 



*Fig. 129. Stab-culture of Bacterium campestre in nutrient gelatin o to phenolphthalein, after 12, 28 and 46 days 

 at about 23 C. Only upper part has liquefied. Lower part has not liquefied even along needle-track where some 

 growth has taken place. In lower tube there is a heavy yellow precipitate at bottom of liquefied clear gelatin. Inocu- 

 lated June 5, 1897. 



