

1905.] On Vegetable Assimilation and Respiration. 405 
tubes, from the COz-generator to the chamber (A), and from the chamber 
to the Pettenkofer tubes (B); the fine rubber tubes (E) and (F) to the back 
of the chamber, containing the electric wires; an inlet tube (C) from the 
water supply, passing to the bottom of the bath, and wide enough to carry a 
rapid circulation of water; holes (D) for the outflow of the water, which was 
allowed to stream down the back of the bath; and (G) a thermometer, 
to indicate the bath-temperature. The air-current which enters at (A) 
passes through a thrice bent glass tube, to give it time to acquire the bath- 
temperature. The end (H) of this system of glass tubes can be opened when 
required to let water into it, and this water gravitates at once into the 
chamber to keep up the supply for the leaf. 
The air-current leaving the leaf-chamber by the tube at its apex, passes 
through a tube of calcium chloride to be dried; condensation in the cooler 
tube outside the bath is thus prevented. 
The water-bath fits into a wooden support resembling an upright box 
without front or top, painted black inside, and hinged by its lowest edge 
to a substantial base-board. This hinge permits movement in a vertical 
plane ranging from the horizontal to the vertical positions. The base-board 
can be rotated horizontally on a central pivot fixed on the table. By these 
two movements the bath with the contained leaf-chamber can be adjusted by 
hand so as to be kept at right-angles to the incident sun’s rays throughout an 
experiment. 
The necessity for tilting the bath to follow the vertical displacement of the 
sun made it difficult to heat from beneath with a burner; the heating was 
therefore achieved by carrying the water-current, before it reached the bath, 
through a laboratory water-heater of the horizontal flanged-tube pattern. By 
varying the amount of gas burning and the rate of the water-flow any 
temperature above the summer temperature of the running water could be 
obtained in the bath. 
The water-heater was carefully boxed in so as to be protected from the 
wind, and a subsidiary thermometer was placed in the water-current close to 
the exit from the heater. This did away with the risk of excessive alterations 
of temperature, as it gave immediate notification of the full effect of any 
readjustment of the heating long before the large mass of water in the bath, 
and the bath-thermometer, reached the corresponding temperature. 
As the leaf in its chamber was only two inches from the front of the bath, it 
received, when exposed freely, the diffuse light from more than a third of 
the hemisphere of the sky, which at this level, on the roof, is very little 
interrupted by the tops of adjacent trees. 
When it was desired to expose the leaf to the sunlight alone without the 
