Smith—-The Organization of the Colony . 1171 
Only one species of Tetracoccus is known, according to 
'Will© (43). Tike cell dimensions of the form that I have 
studied are well within the limits set by West (42). 
Tetradesmus wisconsinensis Smith was originally described 
from the same material that was used for the study reported in 
the present paper. 
Material and Methods 
The forms, work upon which is reported in the present paper, 
were isolated by the general method first used by Beyerinck (5), 
and later by Chodat and G-rintzesco (11'), Chodat (8) (9), 
Grintzesco (17) (18), Artari (1) (2), and others. 
The medium used was. a 2.0 per cent Knop’s solution in 2.0 
per cent agar. The tube containing the nutrient agar was 
melted in the usual manner, and then a drop of water contain¬ 
ing the algae was added. In practice I have found it better to add 
very small portions of water, even inoculating the melted agar 
with a sterile needle dipped in water containing the algae, 
rather than to use the ordinary method of successive dilutions. 
The agar is then poured into Petri dishes in the customary 
manner. 
The growth of bacteria in the medium is comparitivelv rap¬ 
id: the algal colonies grow very slowly. The rate of growth 
is influenced hv heat and light. Ward (40) has shown that 
direct sunlight kills many algae, hut that they grow luxuriantly 
in diffuse light. Grintzesco (18) also found that growth was 
faster when the cultures were exposed continuously to an elec¬ 
tric light than when they were exposed to daylight. The 
same author found 20 degrees centigrade to be an optimum 
temperature for the growth of Scenedesmus acutns. 
Under ordinary summer conditions, the algal colonies become 
visible as small green dots in from eight to twelve days. All 
algal colonies do not develop at the same rate, and I have usually 
found that the first colonies to appear were those of Chlorella 
and other simple forms. For this reason it is best to let the 
plate cultures stand twenty days before trying to isolate the 
