97 



(ibtaiued in four Iioius. This gsis was so rich In oxygen that a glowing 

 splinter thrust into the tulie hurst into tianie with an explosive snap. The 

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

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

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

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

 tity being insufficient for the spark test. With none of the i)lants used was 

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

 -ccond day. 



Similar tests wei'e made with Jtlclilafus officinalis, Trifcliinii jiratcnse. 

 Trifoliiiiii repcns, Ijictuca cfiiutdcnf:i><, Arctiiini ))ii)iiis and ^'cixta catariit. 

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

 the first day. Lactura and Arotiiun evolved very little gas during the sec- 

 ond day and both showed consideral)le maceration after sixteen to twenty 

 hours in the apparatus. With Nepeta the evolution of gas appeared to be 

 more rapid than in Melilotiis, thougli this might have been due to differ- 

 ence in light intensity or l>ecause of a greater leaf surface being exposed. 

 Xo accurate measurements of leaf surface were made in any of the tests, 

 iiut approximately tlie same leaf area was used in each case. In all the 

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

 lint in e\'ery case there was a free evolution of tlie gas and not at all the 

 tiny quantities that Doct(jr Ganoiig suggests. In all cases, too, the gas 

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



It will I)e noted that all the plants named above, have either a hairy 

 I'V 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- 

 posed to bright sun this film grows thicker and thicker until it becomes a 

 bubble of considerable size. After a time a portion of the bubble breaks 

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

 while the plant is in bright sunlight. 



In the case of Nepeta and Arctium there are a number of minute 

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

 forming more 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 Melilotus, TrifoUum 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—3321.3 



