SOIL-WATER CULTURE TECHNIQUE 23 



to the influx of water by capillary force. Then also the blowing 

 out of the droplet of water with the algal cells is easier than with 

 long narrow pipettes as previously recommended, so that a piece 

 of ordinary rubber tubing, closed at one end with a glass stopper 

 provides sufficient expulsion. This is removed for drawing out of 

 capillaries. 



The isolation of algal cells is performed by first holding the 

 tip of the capillary over the fluid so that its position is just per- 

 ceived, and then quickly lowering its open end so that the cell is 

 drawn in, and then immediately lifting it out again. This manip- 

 ulation can be repeated several times until up to ten cells have 

 been taken up. They are then blown into a few drops of sterile 

 fluid contained in a watch glass which has been sterilized in a 

 Petri dish. By repeating the process once or twice the cells are 

 isolated from other organisms and can then be transferred singly 

 into soil-water tubes. As a washing fluid dilute soil extract is 

 generally suitable. 



Cultivation 



Because primary cultures are inoculated with one cell only to 

 secure homogeneity, it takes a long time before multiplication 

 develops visible evidence of growth even under favorable culture 

 conditions. In most instances development should be detectable 

 after a month, but no result can be expected if growth is not seen 

 after two months. Primary cultures as a rule are not suitable for a 

 detailed study of the alga because there are too great differences 

 between the oldest and the youngest cells. Subcultures insem- 

 inated with as much material as available are much better when 

 inspected young. Frequent subculturing is beneficial for quickly 

 growing species. 



No artificial light is as good as daylight near a north window. 

 This of course is not sufficient for many algae in British climate 

 during a great part of the year. A south window with tissue paper 

 as a protection against direct insolation will often serve well 

 during winter. In respect to artificial light I still find an ordinary 

 500-Watt bulb with water screen better and more economical 

 than luminescent tubes. The heat radiation of the latter is by no 



