20 THE TRANSPIRATION OF WATERY FLUID BY LEAVES. 



tion at first was merely to repeat some of the more important experiments 

 made by other observers on the transpiration of watery tkiid. The 

 experiments, which numbered about 100, were conducted in the labora- 

 tory of tlie Royal Agricultural College, kindly placed at the author's 

 disposal by Professor Church. In all the experiments Prinins Lcmroce- 

 rasiis was used. The whole experiments may be arranged under eleven 

 heads. I. Quantity of water in the leaves of the Laurel. This was deter- 

 mined by drying the leaves in the water bath at a temperature of about 

 100° Cent, until they ceased to lose weight. The total weight of water 

 determined in this manner was found to be equal to (1) 63"4 per cent, of 

 the total weight of the leaves employed. — II. Quantity of water which 

 can be removed from the leaves by calcium chloride and sulphuric acid 

 in vacuo. 



(2.) Quantity of water which can be removed from the leaves by cal- 

 cium chloride, 5'08 per cent. 

 (3.) Ditto, sulphiu'ic acid in vacuo, 6'09 per cent. 



By placing leaves in the sun, and allowing the fluid to transpire, only a 

 limited quantity could be obtained, equal to (4) 5"8 per cent. — III. 

 Amount of transpirable fluid in the stem and leaves at a given time. The 

 uniformity of the results obtained above led to the conclusion that all the 

 fluid in the plant did not, at a given time, exist in a transpirable condi- 

 tion. If, therefore, a quantity of fluid was transpired, and the loss sup- 

 plied with some fluid easily detected in the plant, it followed that by 

 causing, say, 7 per cent, of fluid to be transpired, the fluid used to 

 replace that transpired ought to be found in every part of the branch. 

 Lithium citrate in dilute solution was employed for the purpose. The 

 lithium was then tested for by means of the spectroscope, and it was 

 found that when 7"58 per cent, of fluid had been transpired by the leaves, 

 the lithium could be detected all through the branch. The amount of 

 transpirable fluid in the stem and leaves seems, therefore, to be about 

 (5) 6 or 7 per cent., while the fluid in relation to the cell-sap will be (6) 

 from 56 to 57 percent. — IV. Rapidity of transpiration in sunlight, diffused 

 daylight, and darkness. Three sets of experiments were made, each 

 lasting for one hour. In another series the branches were placed in dark- 

 ness for forty-eight hours. The results are as follows : — 



(7.) Rapidity of transpiration in sunlight, one hour, 3-03 per cent. 

 (8.) Ditto, diffused daylight, 059 percent. 

 (9.) Ditto, darkness, 0'-±5 per cent. 

 Branches placed in darkness for forty-eight hom's in ^n ordinary atmosphere 

 gave oft" a mean of (10) 13-47 per cent, in forty-eight hom-s. — V. Amount 

 of fluid transpired in a saturatetl and in a dry atmosphere in the sun and 

 in diftused daylight. In conducting these experiments, care was taken 

 to have them done at the same time, so that the external condition of 

 light, temperature, etc. would be the same. The saturated atmosphere 

 was obtained by placing the branch to be experimented on under a 

 l)eaker resting in water. To one side of the beaker a large piece of wet 

 filter-i)aper was attached. The dry atmosphere was obtained by placing 

 the branch under a bell-jar standiiig over mercury. Two tubes entered 

 the jar, both connected with U tubes containing sulphuric acid. To one 

 tube an aspirator was connected, and a gallon of dry air [>assed through 

 tlie apparatus during the experiment. 



