[Vor. 1 
30 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
Material to be Plated.—The alga to be plated should be 
collected with as little adhering foreign matter as possible. 
If it is à filamentous form which can be manipulated with a 
platinum needle, it can be materially cleansed by washing 
in sterilized nutrient solution such as is used in the preparation 
of the agar. If the alga is a unicellular form, little can be done 
in the way of preliminary cleansing. Dilutions are made in 
the usual manner, the degree depending upon the number 
of algal organisms present. Тһе degree of dilution will depend 
in part, also, upon the number of bacteria and fungi present 
as determined by microscopic examination. It must be re- 
membered that the alge grow more slowly than most bacteria 
and fungi, and that unless the dilution, from the standpoint of 
the total number of organisms present, is great enough, the 
spread of bacterial and fungal colonies may be so great as to 
таКе the transfer of the later-appearing algal colonies impos- 
sible without contamination. 
The material should be introduced into the tube of liquid 
agar while the latter is still a few degrees above its congealing 
point, in order that the inoculated tube may be vigorously 
shaken for some time before its contents are poured into the 
Petri dish. Іп this way the algal cells are freed of large numbers 
of either accidentally or regularly adhering bacteria. 
Incubation and Transference.— The plates, after the agar has 
solidified, should be turned upside down in order to prevent 
the moisture which condenses on the cover from dropping, 
and spreading bacteria over the surface of the agar. Failure 
to do this often renders large numbers of platings worthless. 
The most favorable place to keep plates is in the light of a 
north window; and, as plates frequently remain under obser- 
vation for many weeks, it is further desirable to have them in 
a glass case to prevent outside contamination. In general it is 
not advisable to cover the plates with bell jars, as it increases 
the humidity in the Petri dishes and accelerates the growth 
of moulds present as contaminations. The plates should be 
examined frequently and when rapidly spreading colonies of 
fungi or bacteria appear, these should be dissected out in order 
to save the remainder of the plate. 
The length of time necessary for the appearance of the algal 
