Page:Journal of botany, British and foreign, Volume 9 (1871).djvu/30

 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 the 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 the apparatus during the experiment.

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