62 BOTANICAL GAZETTE [july 



simplified by using an ordinary bottle and placing in it a small 

 vial containing indicator, into which dips the tube which is 

 attached to the bulb. It is always advisable to have a con.trol 

 in the light without a plant and a control in the dark containing a 

 plant similar to the one used in the experiment. For the measure- 

 ment of respiration the procedure is the same, except that no CO2 

 is introduced at the start and that phenolsulphonephthalein or 

 a similar indicator is employed. For quantitative work on respira- 

 tion it may be desirable to have the bubbling go on without 

 interruption. This may be accomplished by an excentric wheel 

 driven by a small motor, and so arranged that at every revolu- 

 tion it compresses the bulb sufficiently to send a few bubbles 

 through the liquid.' 



Whenever it is desirable to remove the accumulated CO2 the 

 tubes D and E are opened and a current of air is run through 

 the chamber (by means of an attached aspirator or syringe). The 

 tubes D and E are then closed and the gas is bubbled through the 

 indicator until equilibrium is established. The apparatus is then 

 ready for starting a new experiment. 



In the same manner air charged with volatile substances 

 (ether, chloroform, etc.) may be introduced in order to study 

 their effect upon photosynthesis and respiration (substances hav- 

 ing a pronounced acid or alkaline reaction or a strong buffer 

 effect are unsuitable for this purpose). 



Summary 



The photosynthesis and respiration of land plants may be 

 studied by placing them in a chamber in which the gas can be 

 made to bubble through an indicator. The changes in the color 

 of the indicator indicate the changes in the tension of CO2. 



The method is so simple and convenient that it is adapted to 

 classroom demonstration as well as to investigation. 



Laboratory of Plant Physiology 

 Harvard University 



» See OsTERHOUT, W. J. V., Jour. Gen. Physiol, i: 17. 1918. 



