1914) 
SCHRAMM—PURE CULTURE METHODS IN THE ALGÆ 41 
that the concentration of the mineral nutrients employed in 
the agar, 0.1 per cent, is quite sufficient to bring about coagu- 
lation. 
After it had become probable that no blue-green alga, in 
the ordinary vegetative condition, could be isolated by the 
usual plating method, tubes containing from two to three 
inches of solid, sterile, synthetic agar were inoculated at the 
surface with a species of Oscillatoria. The tubes were then 
completely wrapped in black paper, leaving only the very 
bottom exposed to the light, and inverted. It was hoped that 
in the rapid growth of the alga through the agar, the bacteria 
might be left behind. The growth toward the light in some 
cases amounted to eight mm., and more, per day. When the 
growth had approximately reached the bottom of the tube, 
the end of the latter was broken away, the surface of the agar 
seared, and transfers made from the interior of the agar plug. 
Although the experiment was repeated many times, and a 
total of at least fifty transfers made, a pure culture was never 
obtained, bacteria always being present. Large Petri dishes, 
containing a layer of sterile synthetic agar, were then inoculated 
at one edge with a species of Oscillatoria, and the dishes so 
placed that the point of inoculation was farthest away from 
the light. Тһе alga grew rapidly (on the surface of the agar) 
toward the light, and just before reaching the opposite edge of 
the dish, transfers were made from the farthest advanced 
filaments. Although transfers to fresh agar surfaces were 
continued to the number of six, a pure culture was never 
obtained. 
The experiment was then repeated, surfaces of silicic acid 
jelly replacing those of agar, with the result that numerous 
pure transfers were obtained from the second plate. A species 
of Microcoleus was obtained in pure culture in an identical 
manner. 
Most members of the Oscillatoriacee are provided with a 
sharply delimited, gelatinous sheath. Reproduction is effected 
by the formation of hormogonia which glide out of the sheath, 
move about slowly for a time, and then come to rest. In 
forms like Microcoleus, Lyngbya, and some species of Oscilla- 
toria in which the hormogonia escape from definite sheaths, 
