Bottomley . — The Root-nodules of My rica Gale. 115 
violet being removed by ethyl alcohol, but retained when treated with amyl 
alcohol. Harrison and Barlow consider this a special differentiating stain 
for Pseudomonas radicicola. 
Pure cultures were also obtained by plating out some of the expressed 
matter from a sterilized nodule on to nutrient agar plates. 
The nutrient material consisted of maltose 1 grm., potassium phosphate 
0-5 grm., magnesium sulphate 0-02 grm., ammonium phosphate 0-5 grm., 
agar 1 grm., and 100 c.c. distilled water. 
The inoculated plates, after incubation for two days at 28° C., showed 
numerous colonies which were round to lenticular in shape, raised, entire, 
viscous, and 075 to 1 mm. in diameter. These colonies corresponded in all 
respects to the characteristic colonies of Pseudomonas radicicola. Micro- 
scopic examination of the colonies showed the typical rod-shaped Bacteria. 
Estimation of Nitrogen Fixation by the Bacteria. 
Cultures of the Bacteria were made in Erlenmeyer flasks of 300 c.c. 
capacity containing a nutrient solution consisting of 100 c.c. distilled water, 
1 grm. maltose, 0-5 grm. potassium phosphate, and 0-02 grm. magnesium 
sulphate. Some of the flasks were inoculated with a loop from the colonies 
on a nutrient agar plate ; others were left uninoculated and formed controls. 
All the flasks were incubated at 25° C. for seven days. During this time 
the contents of the uninoculated flasks remained clear, but the inoculated 
flasks became cloudy. 
Kjeldahl nitrogen determinations of the contents of the flasks gave the 
following average results : 
Control flasks . . . 0-53 mg. N per 100 c.c. 
Inoculated flasks . . 2-58 „ „ 
showing a fixation of nitrogen of 2-05 mg. per 100 c.c. of culture. 
Effect of Nodules on Growth of Myrica Plants. 
To ascertain the effect of the presence of nodules on the growth of 
Myrica plants attempts were first made to strike Myrica cuttings in sand 
watered with nutrient solution; but all ended in failure. 
Excellent results were, however, obtained with young Myrica plants 
procured from Heysham Moss last spring. Some of these plants possessed 
small nodules on their roots ; others appeared to be quite devoid of nodules. 
Six of each were planted out in a greenhouse, in pots containing sterilized 
soil deficient in nitrogen. All the plants with nodules flourished well. Of 
the six plants without nodules, two made no growth for some time, but 
afterwards began to shoot. On examining their roots a few nodules were 
found. Evidently these were already infected with Bacteria, but the nodules 
had been too small to see, when they were planted out." The remaining 
