268 Transactions of the Canadian Institute. [Vol. VII. 



short time. A very dry atmosphere surrounding the leaves will cause 

 such rapid evaporation of the water that there may be no definite 

 reaction either way on some plants. It is not difficult to see that the 

 time required to extract substances in solution osmotically from the leaf 

 tissue will vary with different plants. Both the substance to be diffused 

 and the septum through which diffusion takes place, have to do with the 

 amount diffused in a given time. This process is in accordance with the 

 general laws of diffusion, the solution within the cells on the one side of 

 the septum and the water on the other. All the experiments described 

 show that a substance is actually extracted from the leaf, the time 

 required being different with different plants. 



When the plants were placed under bell-jars to reduce in amount the 

 evaporation from the leaf surface they were under different climatic 

 conditions from the surrounding plants in the open. These differences, 

 however, were not of such a nature as to interfere with the progress of 

 the experiment, as is shown by the numerous controls. During the day 

 time there would be, when photosynthesis is active, a diminished amount 

 of CO., in the air in the jar ; while during the night when photosynthesis 

 is checked, or stopped altogether, and respiration is still going on, there 

 would be an excess of COj in the air of the jar. The action of an 

 excess of CO2 would be to render the water drops clinging to the sides of 

 the jar of an acid quality. 



When the water had evaporated slowly down to dryness upon a 

 glass surface there was always a slight alkaline reaction to the litmus 

 paper. The general results of the experiments with the plant 

 Helianthus (exper. I, II, III), are that distilled water became alkaline in 

 twenty-four hours after being placed upon leaves. The same reaction 

 was found whether the water were placed on the upper or on the lower 

 side of the leaf As the plant was inside a bell-jar, as in experiment I., 

 it was easy to have a leaf touching the moist inside surface of the jar, 

 with a strip of test paper touching both jar and leaf in the presence of 

 water. The strips placed clinging to the inside surface of the moist jar 

 were in fair comparison with that touching leaf and jar, and in the latter 

 case the portion touching the leaf showed the stronger alkaline reaction. 

 This tends to prove that the alkaline reaction is caused by the leaf, and 

 not wholly or in large part by the glass, as was suggested by the writer 

 to have been possible. 



Sachs shows (Bot. Zeit. 1862, p. 257) that the substances contained 

 in the conducting vessels in the stem of the plant, in petioles and in 

 veins of a leaf are alkaline. It is therefore possible that this alkaline 



