96 



howe\er, will not do this when they are immersed in water, bnt it is 

 necessarj' to set up ratlier complicated apparatus." 



Doctor Ganong, wlio may be regarded as an autliority in plant physi- 

 ology, iu commenting ou this experiment criticises severely the statement 

 that land plants may be used. lie says, "An erroneous experiment, given 

 in sevei'al text-books, accompanied by a false illustration, is that one in 

 which leaves of land plants placed under water are represented as giving 

 off bubbles of oxygen which rise through the water. It is true that leaves 

 which are enveloped in a film of air do carry on some i>hotosynthesis under 

 water, but the amount is so small that it is doubtful if any visible bubbles 

 of oxygen are released, the tiny (luantitios being tal<en directly into 

 solution. ""^ 



It is tlic pur])osc (if this jiapor to show that sonic land plants do carry 

 ou photosyntiiesis. when submerged in water, and that for purposes of the 

 experiment descril)ed above, are even liettcr tlian the water jdants ordinar- 

 ily used. 



In Septeinlier of 1011 my attention was called to tlie fact that Mcli- 

 loliis (ilhd. wiien submerged in water, could carry on photosyntiiesis, witli 

 consideiMble evolution of gas. and that the gas is jiarticularly rich in 

 oxygen. .Vt tlic suggestion of I'l'ofessor Howard .1. Hanker a number of 

 simjile iireliminary ('xjierimeiits were carried on to test tlie power both in 

 Molilotus and in several other land jilants. It was intended that more 

 careful exiierimeiits should lie performed Liter to determine the jiercentage 

 of oxygen in tiie gas and the rate of the evolution of the oxygen undei- 

 varying conditions. Wliile this (|nantitative work has not been done, the 

 results so far oiitaiiK-d are so striking as to appeal' of interest and wortliy 

 of note. 



In tlie experiments as iierfornied. a few le:ives of the plant iiiidei' 

 observation, were placed in the usual niainier in ;i glass funnel wliicli was 

 inverted in a large glass jar full of water. A test tube of 30cc. cajiacity 

 was used to collect the evolved gas. ("arbon dioxide was generated by 

 treating ordiii:iry limestone with hydrochloric a<-id. and a stre.-im of this 

 gas was kept bultbling through the water outside the funnel. The whole 

 apparatus was exiiosed to sunlight in a soiitli window. 



With ]\l(lU<it lis iilJiii. using tliree or four vigorously growing shoots. 

 having approximately one linndi-ed leaves, from CO to SOcc. of gas was 



8 O.anonfr. .V Lahoiatdiv Cmirso in Plant T'liysioloii.v. p. lO;!. 



