58 



BACTERIA IN RELATION TO PLANT DISEASES. 



inoculated from young potato cultures, there was in 7 days a very feeble growth restricted 

 mostly to the upper part of the stab and yellow only at the surface. The cultures were fol- 

 lowed for 43 days, but there was no increased vigor of growth ; no crystals, liquefaction, or 

 staining of the gelatin occurred. 



In six tubes of the same gelatin with addition of 1 per cent cane-sugar, growth at the 

 end of 43 days was about double. These tubes were inoculated at the same time from the 

 same cultures as the preceding, and were subject to the same conditions. Even in this 

 medium, growth was rather feeble and there was no liquefaction. Probably the medium 

 was too acid. 



This inference was confirmed by subsequent experiments in the same medium neutral- 

 ized with sodium hydrate. There was a comparatively good growth at the end of 10 days, 

 but no liquefaction. At the end of a month there was a strong growth the whole length of 



the stab, thinning out below, 

 whitish also below (where air 

 was less abundant) and pale 

 yellow in the upper half. 

 The surface growth was 

 paler yellow and more ex- 

 tensive than in the same 

 medium without the alkali ; 

 the nail-head was also 

 sunken into the gelatin a 

 little, as if there had been 

 slight liquefaction. 



Experiments with gel- 

 atin, to which filtered cane- 

 juice had been added, 

 yielded interesting results. 

 In streaks on stock 727 the 

 organism made a fairly good 

 but not a very vigorous 

 growth. On the forty-third 

 day the growth was dis- 

 tinctly yellow (in contact 

 with the air) and at least ten 

 times as abundant as in the 

 gelatin containing peptone, 

 dipotassium phosphate, 

 malic acid, and cane-sugar. The surface growth was restricted (piled up), smooth, wet- 

 shining, and Naples yellow in color. There was no liquefaction. The gelatin was not 

 stained and no crystals were present. Growth started off slowly. The temperature varied 

 somewhat, averaging about 20 C. This stock was prepared as follows: juice of Common 

 Purple cane 250 c.c, distilled water 750 c.c, Nelson's No. 1 gelatin 100 grams. On the 

 same stock rendered slightly alkaline (to phenolphthalein) by the addition of NaOH (stock 

 741) there was only the least trace of growth in 5 out of 6 streak cultures. On the sixth 

 streak, in course of 2.5 months, the organism succeeded in getting a start, but piled up locally 

 in a very striking manner. There were many of these bacterial masses, most of them 

 approximately circular, 1 to 8 mm. in diameter, and some of them 2 mm. high. Their color 

 was about Ridgway's maize yellow. There was no liquefaction of the gelatin. Six stab 



Fig. 32.* 



*Fig. 32. Streak-cultures of Bacterium vascularum on potato agar. Subcultures from three different plants (7, 9, 

 and 1 1), inoculated Feb. 6, 1903. Streaks made Nov. 2, 1903. Photographed after several days. 



