97 



obtained in four lionrs. Thi>! gjis was so ricli In oxygen tliat a glowing 

 splinter thrust into the tube burst into flame with an explosive snap. The 

 same leaves were left in the apparatus and on the second day yielded 

 more than 30ce. of gas, giving a good spark test. On the third day, how- 

 ever, the water in the y^iv showed green and the plants were becoming 

 macerated. Only a very little gas was evolved during this day, the quan- 

 tity being insufficient for the spark test. With none of the plants used was 

 any gas obtained after the second day, and sometimes only a little on the 

 second day. 



Similar tests were made witli Mclilotiis offichmUs, TrifcIiuDi pratcusv, 

 Trifoliuiii rcpciis, Liutuca va]i(i(h'iisis, Aictiiini iiiiniis and Xcixta cut'irUi. 

 With all these plants a good evolution of gas was obtained, at least during 

 the first day. Lactuca and Arctuim evolved very little gas during the sec- 

 ond day and both showed considerable maceration after sixteen to twenty 

 hours in the a])paratus. With tfepeta the evolution of gas appeared to be 

 more rapid than in McliUifiis, though this might have been due to differ- 

 ence in light intensity or because of a greater leaf surface being exposed. 

 No accurate measurejnents of leaf surface were made in any of the tests, 

 but apprctximately the same leaf area was used in each case. In all the 

 plants used, except Xepeta, there was less gas evolved than with Mclilotus, 

 but in every case there was a free evolution of the gas and not at all the 

 tiny quantities that Doctor Ganoiig suggests. In all cases, too, the gas 

 gave a very good spark test, showing it to be very rich in oxygen. 



It ^^■ill be noted that all the plants named above, have either a hairy 

 or waxy covering to the leaves so that they do not become wet when im- 

 mersed in water but are really enclosed in a thin film of air. When ex- 

 [tosed to Ijright sun this film grows thicker and thicker until it becomes a 

 l)ubble of considerable size. After a time a portion of the bubble breaks 

 oft" and rises through the water into the test tube, this process continuing 

 while the plant is in bright sunlight. 



In the case of Nepcta and Arctiiiiit there are a number of minute 

 bubbles formed on the surface of the leaf, these being more numerous and 

 forming juore rapidly on the under side. These bubbles increase in size, 

 merging together to form large bubbles until they become so large that 

 portions break off and escape into the tube. With BIcUlotiis. TrifoJiuiii and 

 Lactuca the film of air seems continuous and becomes a large bubble 

 which practically encloses the leaf. The bubbles which rise into the test 



7—33213 



