1910. | On Vegetable Assimilation and Respiration. 377 
raising or lowering the pipettes, by sliding up or down on the board L 
the slips of wood K to which the pipettes are attached. 
Most of the disturbances in the rate of flow were due to the liberation 
of tiny bubbles from the liquid in the effluent tube (7). The impediment 
to flow which they caused was removed by shaking the tube and working 
the bubbles up into the blind arm M.* 
(c) The Bath and Temperature Regulation—The temperature of the 
cubical copper bath of water in which the chamber was entirely immersed 
was kept constant by a thermostat when temperatures above that of the 
laboratory were wanted. (Only the burner below the bath is shown in 
the figure.) Temperatures between those of the laboratory and the water 
supply could be kept constant merely by a regulated circulation of water 
through the bath. The lowest temperatures used were obtained by careful 
regular additions of small quantities of ice. 
In the front of the bath is a large glass window J for lighting the 
assimilation chamber, and in front of the window a screen of rapidly- 
circulating cold water to cut off the heat of the illuminating burner Q from 
the bath. This screen is made by a rectangular brass frame fastened to 
the front of the bath and carrying a second glass plate N. The space 
between J and N is full of water; O is the inflow and P the outflow for 
this water screen.t 
(d) Light for Assimilation and its Regulation—All the experiments were 
carried out with a special artificial light, that of the triple Keith high- 
pressure burner used in this laboratory since 1903. The burner Q was 
placed on a small wooden table fixed in front of the bath. The intensity of 
the light is determined by its distance from the assimilating plants. When 
the fronts of the nearest pair of mantles are 130 mm. from the front of the 
assimilation chamber, the arbitrary value of 6 has been assigned to the 
light-intensity.t From this standard the intensity in other positions can be 
calculated. 
(e) Lhe Supply of CO Solution.—Tap-water that had been boiled for some 
time to remove the CO2 and the calcium carbonate was used as being more 
* There is a small omission in fig. 1. The tube rising vertically from & should be 
continued up to a free end closed by a tap, used for sucking out obstructing bubbles, and 
the tube z should be attached to a lateral branch below the tap. Further the part of 
tube 6, 6 represented as rubber should really be all glass. 
t+ The screen carries about 1 inch thickness of water, and the front glass is not 
cemented in watertight, but pressed firmly against the metal rim all round by corks 
between it and the bath. It is therefore easy to replace if cracked, and the very 
moderate leakage trickles into the trough below the bath and is carried away at I. 
¢ See Matthaei, ‘Phil. Trans.,’ B, 1904, p. 59. 
