28 BOTANICAL GAZETTE | JANUARY 
yellow tinge which overtakes all old cultures. Some of the 
species, as for example 4. 77. putridus, are unable to grow in 
Uschinsky’s medium, and the tubes, although inoculated from a 
young active culture, remain perfectly clear. There is some lack 
of uniformity in regard to the behavior inthis medium. J. vin- 
dans and B. fi. tenuis, for example, will sometimes multiply and 
produce considerable turbidity without forming pigment, and at 
others, under apparently identical conditions, will refuse to grow 
at all. The presence of glycerin is one of the unfavorable factors. 
If the medium be diluted 1:5 or 1:10, all of the species are able 
to grow and produce pigment. 
A medium somewhat similar to Uschinsky’s, but simpler, 
was compounded by Frankel.*® This consisted, in its final modifi- 
cation, of sodium chlorid 0.58", ammonium lactate 68", asparagin 
4", neutral sodium phosphate 28", dissolved in 1000°¢ of water. 
The solution was either amphoteric or slightly acid, and was made 
slightly alkaline ‘“‘with a small quantity of caustic soda.” In 
my early experiments all the species grew quite luxuriantly in 
this medium, but never produced any fluorescence, although the 
old cultures usually had a yellow tinge. The reason for this 
failure to produce pigment might at first be supposed to lie in 
the absence of sulfate, especially since color is developed when 
sulfate is added to Frankel’s medium. But that this is not the 
whole explanation is shown by the fact that, if the original 
medium was diluted 1:10, a very fair development of pigment 
took place. Investigation showed that some of the ingredients 
of the solution were not perfectly pure, but contained a trace of 
sulfate. The quantity of sulfate present, however, was not suf- 
ficient to permit of pigment production in the strong solution, 
although one-tenth of the same quantity was sufficient to permit 
of pigment production in a less concentrated medium. If 
Frankel’s medium be prepared with perfectly pure chemicals no 
pigment production occurs even when the solution is diluted. 
The effect of concentration is well shown also in experiments 
made with solutions of high phosphate content. In solutions of 
*® Hyg. Rundschau 4:700. 
