214 PHYSIOLOGY OF NUTRITION. 



Quantity of water (expressed 

 Kelative number in grams) transpired 



of stomata. in twenty-lour hours. 



( above 10 0'48 



Atropa belladonna. . \ 



( below 5o . . 0*60 



AT . .. ,. I above 15 . . O57 



JN icotiana rustica . . 1 



* below 20 . . 0'80 



( above . 0'20 



Tiha europsea . . . < 



) below 60 . . 0-49 



In order to repeat Garreau's investigations, we fit up the 

 apparatus represented in Fig. 80. Two similar bell-glasses, of 

 different size according to requirements (about 40-80 mm. in 

 diameter, and 100 mm. in height), are applied to the upper and 

 under side of the same leaf, and cemented air-tight. I have found 

 a mixture prepared by melting together 2 parts of olive oil, 1 part 

 of mutton suet, and 1 part of wax, very serviceable as a cement. 

 If the temperature in the neighbourhood of the apparatus is 

 relatively high, e.g. over 20 C., a smaller proportion of olive oil 

 must be used. The bell-glasses must be tubulated, so that we can 

 attach to them the two oil manometers, m and m 1 . Lastly, within 

 each bell-glass is placed a tube filled with Calcium chloride, g, g'. 

 The increase in weight of these tubes indicates the amount of 

 transpiration from the leaf surfaces. It is obvious that we must 

 experiment not with cut-off leaves, but with leaves remaining 

 intact on the plants. In an investigation conducted under my 

 supervision with Begonia, using bell-glasses 42 mm. in diameter, 

 the following results were obtained : In four hours, at 20 C., 

 0'0075 gr. of water evaporated from the upper side of the leaf, 

 while the under side gave off 0*0520 gr. 



Stahl 2 has recently made us acquainted with a method of 

 research (Cobalt test), which serves excellently for many experi- 

 ments on transpiration ; and may also be employed to show that 

 the cuticular transpiration falls far behind the stomatal tran- 

 spiration. Swedish filter paper is impregnated with a 4-5 per 

 cent, aqueous solution of Cobaltous chloride, and dried in an oven 

 or in the sun. We still further dry a piece of the Cobalt paper 

 over a spirit flame or gas flame so that it appears intensely blue, 

 and then lay it on a dry sheet of glass. On the paper we place a 

 leaf of Phaseolus multiflorus, and cover this with a second piece 

 of the dried Cobalt paper and a second sheet of glass. If the leaf 

 was perfectly fresh, and had been exposed to the sunlight before 



