26o Transactions of the Canadian Institute. [Vol. VII. 



this decomposition COo may be furnished to the plant. It may be that 

 the chemical action resulting in the formation of calcium oxalate in the 

 leaves of some plants, and calcium carbonate in others, results also in 

 a liberation of COo. 



It has been observed by (Senebier t. 3, p. 98) Morozzo, that dew- 

 drops, remaining upon the leaves until late in the morning, have an acid 

 reaction upon test paper, and that this reaction is due to CO2 contained 

 in the dew-drop. Senebier analyzed dew and found that when treated 

 with lime-water it gave a flocculent precipitate, which when tested with 

 HjSOi produced an effervescence of COj. He concluded, however, that 

 the dew-drop is always a deposition from the atmosphere, and that it 

 occurs in drops for the same reason that water spread upon an oiled 

 surface will collect in drops. He collected dew in large quantity and 

 made some analyses which are rather striking. From 3791 kilos of 

 filtered dew, he obtained 2276 grams of a solid as a residue from the 

 evaporation of the water, and, after treating this residue with alcohol, 

 then filtering, he obtained as a solid 603.74 milligrams ; on dissolving 

 this in acetic acid, he obtained 421.29 milligrams of an insoluble white 

 substance which he concluded was CaSOi. From these results we may 

 conclude that, from the amount of dew he collected, he obtained 182.45 

 milligrams of a carbonate, probably CaCOj. He believed the dew to 

 contain an acid carbonate, as did Van Tieghem. He found also that if 

 he first filtered the dew he got less effervescence of CO2 when treated 

 with H0SO4. 



In order to test the effects of a dry atmosphere upon leaves holding 

 dew-drops, a number of leaves were taken in early morning and placed 

 immediately in a dr\' atmosphere which produced a rapid evaporation 

 of the drops. On examination it was found that a slight deposit of a 

 whitish substance was left upon evaporation. This result showed 

 clearly that a saline substance had been dissolved in the dew-drop. 

 At the time of collecting the leaves for this experiment, other 

 plants of the same species were marked for observation later. In 

 the case of these plants no deposit was found. This experiment was 

 repeated six times during the summer with practically the same result. 

 The substance contained in the dew-drops must have been largely, if 

 not wholly, extracted from the leaves of the plants. These experiments 

 indicate also, that under favourable circumstances, leaves resorb the 

 saline substance contained in the dew ; and there is a suggestion also 

 that some of the dew-water may be absorbed in the process. 



As the dew experiments seemed to indicate that saline substances 



