[Vor. 1 
34 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
the vegetative cells can be so readily freed from adhering 
bacteria. But its general applicability to other forms justifies 
its mention at this place. Chlorella, like many other genera 
of the Protococcales, forms non-motile endogenous daughter 
cells which remain enclosed in the mother wall for varying 
lengths of time. The enclosed daughter cells are in all cases 
free from adhering bacteria. A group of daughter cells still 
enclosed within the mother membrane may be removed by 
means of a capillary pipette to a drop of sterile water, and from 
here to a succession of others until all readily removable bacteria 
have been left behind. The last transfer should be made to 
a drop of sterile water on a small sterile cover glass. By а 
slight pressure of a second cover glass, the mother membrane 
may be ruptured, liberating the enclosed, bacteria-free cells. 
The two cover glasses should then be introduced into a tube 
of liquid agar, the latter shaken vigorously, and finally poured 
into a Petri dish. Frequent isolations have been made in this 
way, and its importance in forms whose vegetative cells cannot 
be freed from adhering bacteria, and which do not form motile 
spores but only non-motile endogenous daughter cells, can 
hardly be overestimated. 
Pleurococcus vulgaris Menegh.—The majority of Plewrococcus 
cells, when thoroughly washed, will be found free from bacteria. 
A difficulty which frequently arises is that the alga grows so 
very slowly that fungi—which are persistently present in Pleu- 
rococcus cultures—take entire possession of the plates before 
a transfer can be effected. But with careful searching, minute 
colonies—often consisting of but a few cells—can usually be 
found and successfully transferred. The transferred colony, 
however, usually makes extremely slow progress in its growth 
on agar. Much better results are obtained when transfers 
are made to evaporimeters (as devised by Livingston (15)) 
supplied with the mineral nutrient solution. 
Scenedesmus sp., and Kirchneriella sp.—Both of these species 
were obtained in pure culture by washing and diluting clean, 
concentrated material іп sterile mineral nutrient solu- 
tion, and then plating. The great majority of the colonies 
of both species were contaminated with bacteria, pure colonies 
being very rarely found. This fact, together with the gelatin- 
