64 CHAP. VIII. CHANGE IN PHOTOSYNTHETIC ACTIVITY 



had been from 136 to 27, on the removal of the ether the 

 activity was restored to 130, which is practically the same 

 as the normal at the beginning. 



Effect of alcohol. — The effect produced is similar to that 

 of ether. The normal period of bubbling in a vigorous 

 specimen was 13 seconds. One per cent, of alcohol in- 

 duced a depression which increased with the period of 

 application. The bubbling-period was thus prolonged from 

 13 to 77 seconds in the course of 5 minutes. 



Effect of Poisons 



Formaldehyde. — A solution of formaldehyde acts as a 

 very effective poison on various activities of plant-life. It 



Fig. 16. Effect of Application of o-oi per cent. Solution of 

 Formaldehyde on Photosynthesis 



Normal period 27 seconds, prolonged to 287 seconds after 

 application for 16 minutes. 



arrests the rhythmic pulsation of the Desmodium leaflet, 

 and I have recently discovered that the application of this 

 solution to the root or to the cut end of the stem arrests and 

 permanently abolishes the ascent of sap. 



On applying o-i per cent, solution of formaldehyde to 

 Hydrilla, the evolution of oxygen was found to be imme- 

 diately arrested. I next supplied a very dilute solution 

 of o-oi per cent, to a fresh specimen. This caused a con- 

 tinuous diminution of activity, the normal period of bubbling 

 of 27 seconds being prolonged in the course of 16 minutes 

 to 287 seconds, culminating afterwards in permanent arrest 

 (fig. 16). 



Copper sulphate solution. — If a specimen of Hydrilla is 



