86 
BOTANY: OSTERHOUT AND HAAS 
consequently the amount of photosynthesis, can be determined with consid- 
erable precision. 
The amount of photosynthesis is approximately a linear function of the 
change in PH value in the range here employed. 
In order to measure the degree of alkalinity produced by Ulva under the 
influence of sunlight, a piece of the frond was placed in a tube of Pyrex glass 
rilled with sea water and closed as described elsewhere. 2 The tube was then 
placed in a large water bath (the temperature of which fluctuated less than 
1°C.) in direct sunlight. If clouds interfered with the sunlight at any time 
the experiment was rejected. 
Since the plants produce CO2 by respiration this must be taken into consid- 
eration. Experiments were conducted under precisely the same conditions, 
except that light was excluded. They agree in showing that the respiration 
was practically constant. It cannot, therefore, affect the form of the curve 
of photosynthesis. 
TABLE 1 
NUMBER OF MINUTES 
AMOUNT OF PHOTOSYNTHESIS 
PERIOD 
REQUIRED TO 
TOTAL NUMBER OF 
PRODUCE STANDARD 
MINUTES EXPOSED 
ALKALINITY 
Observed 
Calculated 
1st 
35.7 
35.7 
1 
0.92 
2nd 
25.9 
61.6 
2 
2.07 
3rd 
23.3 
84.9 
3 
3.18 
4th 
21.7 
106.6 
4 
4.23 
5th 
20.4 
127.0 
5 
5.23 
6th 
20.3 
147.3 
6 
6.22 
7th 
20.5 
167.8 
7 
7.22 
Average of 5 experiments at 27°=±=0.5°C. 
In each experiment the procedure was the same. Freshly collected Ulva 
(young, dark green fronds not more than 3 or 4 inches long) was placed over 
night in running sea water and covered so that in the morning no light could 
reach it. In starting an experiment the Ulva was placed in a closed tube in 
sea water containing a trace of alcoholic phenolphthalein and exposed to light 
until a definite shade of pink was produced. 4 This shade of pink matched 
that of a standard buffer solution (whose PH value was determined by the 
gas chain) containing the same concentration of indicator as the sea water 
(and observed in a Pyrex tube of the same size). 
When the standard shade was attained, the time of exposure was noted. 
The sea water was then poured out of the tube containing Ulva (the last drop 
being removed by shaking), fresh sea water was added, and a new determi- 
nation was made of the time required to attain the standard shade. 
The results obtained are given in table 1 (average of five experiments). 
The table shows that the time required to reach the standard shade steadily 
diminishes until a constant value is reached. 
