Smith—The Organization of the Colony . 1173 
the method of inoculation directly on the agar slant is to be 
preferred. 
There is more or less confusion in the use of the term “pure 
culture.” According to the usage of some authors, a pure cul¬ 
ture is one that contains only one algal species ; others under¬ 
stand it to be a culture of a single algal species that is also free 
from other organisms, including bacteria and fungi. To dif¬ 
ferential between the two I propose the term unialgal culture- 
to designate one which contains but a 1 single species of alga, but 
which may contain other organisms. The term pure culture is- 
reserved for one which contains a single species of alga, and is- 
absolutely free from all other organisms. 
The second series of Petri dish cultures would then be unial¬ 
gal cultures. After allowing these cultures time to develop, 
single colonies are again lifted out and inoculated on agar 
slants. The colonies should be removed from these cultures as 
soon as they become visible. This work has usually been done 
under a Zeiss binocular microscope. The work should be done 
in a special room where transfers are made, since any infection 
is fatal at this stage. By this method very small colonies are 
obtained, and the smaller bacterial and fungus colonies, which 
would ordinarily be overlooked, can be seen. 
Almost all investigators who have worked with pure cultures 
have noted that algae develop faster in a medium containing 
a small percentage of glucose than one which does not. Ac¬ 
cordingly, a third series of cultures is made by inoculating an 
agar medium, to which has been added 1 per cent of glucose, 
with colonies from the unialgal cultures. This series is made 
on agar slants instead, of Petri dishes. There are two advan¬ 
tages in the use of this medium. The glucose favors the devel¬ 
opment of fungi and bacteria, so that, if there are any in the 
culture they will soon appear. At the end of three or four days 
the infected cultures can easily be separated from those that ap¬ 
pear to be pure. Tn general, in spite of all possible precautions, 
many cultures will be infected. For the inoculation of the 
unialgal cultures from the Petri dish, it is usually best to 
