On Vegetable Assimilation and Respiration. 375 
control, so that the interaction of these different factors can be directly 
investigated. 
The results obtained by this method in a critical investigation of the 
relation between COs-supply and assimilation will occupy the next paper 
of this series. 
Section I.—THE APPARATUS. 
The apparatus is schematically represented in fig. 1. The current of 
CO.-laden water flows by gravitation from the bottle A to the plant 
chamber B situated in the bath C; and, after passing up through it, thence 
by the route d, Y, n, k, into the lower end of one or other of the 
200 c.c. pipettes D and E, finally escaping from them by the overflow tubes 
above into the measuring cylinders F or G. 
The different parts of the apparatus call for description in some detail. 
(a) Lhe Plant Chamber.—The water-plant used is confined in a flat 
vertical glass-fronted chamber of oval outline, 18 cm. long and 11 cm. 
wide, the rim of which is formed by a wrought-iron frame 14 mm. square 
in section (for front view see inset to fig. 1). The iron rim is closed up 
to form a chamber by oval glass plates, back and front, which are luted 
firmly to it by a wax mixture of resin, beeswax, and vaseline. The back 
plate is waxed down permanently, but the front one is removed each time 
to put in material for a new experiment and then refastened. 
The chamber contains a removable oval grid H (made of silver wire, 
with meshes about 6 mm. broad) which hes against the back of the chamber, 
and to this the plant material is tied down with thread. The grid, the iron 
frames, and all metallic parts in contact with the water current, are coated 
with wax to prevent chemical action and possible poisoning of the plant.* 
The iron frame of the chamber is pierced by an inlet tube (0) at its 
lowest point, and by an outlet tube (d) at its highest point. Close to 
the latter is a hole for a thermometer by which the internal temperature is 
determined. Immediately above the inlet tube is a thin sieve-like “ baffle- 
plate,” which stretches right across the opening and causes the inflowing 
water to spread out in all directions, hindering it from rising straight up the 
middle of the chamber. 
(b) The Water-Current.—The effective fall which determines the rate of 
flow of the water-current through the apparatus is the difference in level 
between the mouth of the central tube of the Mariotte’s bottle A and the 
mouth of the upper ends of the pipettes D and E where the water overflows. 
It will become obvious that a uniform rate of flow is of fundamental 
* All parts are of silver or iron ; no copper or brass is present. 
