1916] AYRES—TEMPERATURE COEFFICIENT 67 
The material was collected from floats in a tidal estuary of 
San Francisco Bay. The temperature of the water in which 
Ceramium tenuissimum occurs undoubtedly varies somewhat with 
the change of seasons, but during the winter the temperature is 
practically constant at 9g-10° C. The plants to be brought into 
the laboratory were placed in jars of sea water at the place of 
collection. In the laboratory they were kept at a temperature 
of 12-14°C. by immersing the jars in a stream of running tap 
water. By replacing the sea water occasionally the material was 
kept growing normally in the laboratory for several days. 
Two methods were employed for obtaining and maintaining 
the desired temperatures. In the first place, the temperatures 
were kept constant within an asbestos-lined hood by means of a 
double water bath heated by a Bunsen burner, which was auto- 
matically regulated by a mercury thermo-regulator. By placing 
covered finger bowls containing sea water on shelves in the hood 
above or around the water bath, a considerable number of constant 
temperatures was obtained. The second method consisted in 
placing a double bell jar filled with water over a heavy glass dish 
containing the material in sea water. This apparatus: was then 
placed on top of a glass case which inclosed a 16-candle-power 
incandescent light: A free circulation of air maintained the tem- 
peratures constant to +o0.5°. The various temperatures desired 
were obtained by shifting the position of the bell jar and the 
dish with reference to the light. The results secured by these 
two methods of obtaining constant temperatures agreed so closely 
that both were employed. 
A finger bowl, containing roo cc. of sea water, covered to pre- 
vent evaporation, was brought to the desired temperature and 
maintained constant there for about 30 minutes; a number of 
plants were then transferred directly from the aquarium to the 
finger bowl. At intervals some of the material was removed from 
the finger bowl and transferred to a small quantity of sea water 
at the temperature of the laboratory. ‘‘ Duration of life,” as used 
in table I, was taken as the time for which a given temperature 
must act to cause a change in color of the apical cells of the branches 
from maroon, the normal color, to brick red color, which is char- 
acteristic of dead material. This change in color is due probably 
