98 



tube are large, there being no srrearus or tiny bubbles as in the case of 

 the ^yate^• plants. 



The rate of the evolution of the gas depends on the brightness of the 

 liglit and the supply of carbon dioxide. If a part of the light is shut off 

 the rate becomes slower and the evolution of gas ceases when the light 

 becomes dim. Tlie rate becomes slower if the bubbling of carbon dioxide 

 tlarough the water is stopped. Enough carbon dioxide diffuses into the 

 water from the air for the evolution of gas to go on slowly, but a rapid 

 evolution i.s not obtained unless the water is kept charged with the carbon 

 dioxide. 



In one exi)eriment leaves of MvlllotuH were dipped for an instant 

 into 50% alcohol and then immediately ininuTscd in water. These leaves 

 became \\et, no fihn of air was present and no evolution of gas occuri-ed 

 though the plants were exposed to the sunlight for more than six hours. 



These experiments were i)erformed in May of 1012, after which time 

 nothing further was done except that in October Melilotits and Nepcta 

 wei'e usetl in demonstration experiments before a class. A good quantity 

 of gas was obtained. The rate of evolution was slower than in May, 

 probably due in part to difference in light and part to difference in the 

 condition of the plants. The plants used in May were young vigorous 

 shoots, while only old pliints could be found in October. 



As a plant to use in dcmoMstratiug the cvtihition of oxygen in photi)- 

 synthesis, I am (juite sure tiiat either Mclilotii-s or Xritcta will i)rove en- 

 tirely .satislactdO". They are not only mu'h easier to obtain than the 

 aquatic plants, wliich arc said to lit- necessary for this exiiei-iiiiciit. but the 

 results are more (piickly attained and are more striking tlian is usually the 

 case with the conventional a(|uatics used for this purpose. 



Dcl'ainr I'tiircrsit!/, 



GrccncustJc, lud. 



