392 BOTANICAL GAZETTE [DECEMBER 
violet starts near the inoculation streak and proceeds outward. 
This seems to give evidence of the formation by the organism of 
an acid or an acid acting substance. Such a hypothesis is 
supported by the fact that the red is not produced if calcium 
carbonate is suspended in the medium before it solidifies, thus 
furnishing a substance which will unite it with and neutralize any 
acid as soon as formed. 
The comportment of the blue from agar toward reagents is 
identical with that of the blue from potatoes, and with that from 
gelatin containing glucose, etc. The absorption spectra of the 
different colored solutions from agar seem to correspond to 
those of like color obtained from other media, hence it has not 
been deemed necessary again to reproduce them. 
Generalizations.—It will be noticed that potatoes, glucosed- 
gelatin, agar (especially if glucosed), etc., all yield a blue becom- 
ing violet, then more or less purple. Without taking more space 
to enumerate experiments, it can be stated that no case has yet 
been found where a blue has resulted in the absence of a sugat 
or similarly acting compound. 
Agar-agar is probably closely related to the starches, and 
has been shown by Bauer to contain a compound which 1s 
doubtless a sugar and, in all probability, to give rise to on 
formation of others through the action of acids or alkalies: 
Hence we have here the necessary substances to produce the 
blue pigment. 
The violet colors on different media seem to be due to the 
action of an acid or acid acting substance. As the culture a 
older there is more of this substance formed, and the violet 
changes to purple or to a red. This hypothesis is based 5 ae 
the changes in position and character of the absorption bands ; 
on the comportment of agar cultures containing calcium caf- 
bonate; and on the fact that the addition of acids to the blue 
solutions produce changes in color and in absorption an? 
similar to those noticed in the aging of cultures. This acid may 
Journ. f. prak. Chem. II. 30:367. 1884. See also Lippmann, Chemie der 
Zuckerarten. Braunschweig. 1895. 
