Nov., I92i] LYON COMPARATIVE STUDIES ON RESPIRATION 
459 
solution on the same material in the same tube. For normal respiration 
the material was placed in lo cc. of water to which had been added 5 drops 
of a o.oi percent solution of phenolsulphonphthalein. Both tap and dis- 
tilled water were tried, and as no difference could be noted in the effects on 
the plant, distilled water was used exclusively, since the salt solutions were 
made up in it. This eliminated possible effects of the salts in the tap water. 
Both the water and the salt solutions were brought to the proper al- 
kalinity by the addition of a very dilute solution of sodium hydroxide, the 
same amount being added to each. 
The plants selected were healthy stems, uniform in appearance, which 
averaged from 3 to 4 inches in length. These were kept in running water 
before use (to remove any excess of CO2), and were then coiled and inserted 
in the tubes where the pressure of the coil held them in the middle of the 
tube. This kept them from interfering with the observation of the color 
of the solution (in the lower half of the tube) and with comparison with 
the color of a standard solution. The paraffined rubber tube at the top 
was then tightly clamped off after adding the water plus the indicator. A 
bubble of air, of uniform size in all experiments, was left below the clamp 
to aid in stirring the solution. The pH value of the water was brought to 
a little above 7.88, but it dropped to 7.88 shortly after the plants were 
placed in it. The exact time at which this point was reached was deter- 
mined by matching its color with that of a buffer solution of pH 7.88 (which 
had the same concentration of indicator). 
The contents of the tube were kept in constant motion by gentle stirring 
during the few minutes required for the evolution of enough CO2 by the 
plant to change the color to match that of the second standard tube 
of pH 7.60.^ This range of 7.88 to 7.60 was used in all experiments. In 
getting the normal rate, the amount of material used was adjusted to give 
a period of from 3 to 5 minutes in most cases. 
That no acid other than carbonic was produced was shown by the fact 
that after the plant had changed the color of the indicator solution, it would 
rapidly return to the original color when a current of C02-free air was 
bubbled through it. 
The normal period of respiration for each experiment was first deter- 
mined. It was usually found that this period was practically constant for 
two hours or more, and if this was not the case the material was rejected. 
At least three readings (covering a period of at least 20 minutes) were 
taken, previous to the addition of the salt solutions, in order to establish 
the normal rate. 
The temperature varied from 21 to 25° C. In the course of any one 
experiment, the temperature did not vary more than two degrees. 
The solutions of salts were made up in large quantities and kept in 
^ The source of light was a " Dayhght lamp." Cf. Luckiesch. Science n. ser. 42: 764. 
1915- 
