6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 87 



eter. The details of construction are shown in Figure 2. In order 

 that the various types of hght sources may he conveniently used and 

 a maximum of flexibility obtained, arrangements have been made for 

 both lateral and overhead illumination. Four of the eight faces of 

 the octagon may be covered with glass windows, bolted on with suitable 

 gaskets. The other four sides are double-walled in order to provide 

 for temperature control by circulating water. These are shown cross- 

 hatched, in a portion of the top view. The inner faces of these sides 

 are of polished monel metal, which has the advantage of a fairly 

 permanent polish and a minimum of variation of reflecting power 

 from the visible to the far ultra-violet. Circular openings 14 inches 

 in diameter have been provided in both the top and bottom. This 

 choice of diameter enables one to use the standard front glasses of 

 industrial flood lights for windows. These convex windows are avail- 

 able in pyrex, a matter of considerable importance when dealing with 

 lights of high candle power. Furthermore, through the cooperation 

 of the Corning Glass Works the filters previously described and 

 usually available only in small sizes have been cast in these larger 

 standard molds. It thus becomes possible to secure a color filter which 

 will cover the entire opening. Provided with suitable gaskets two 

 of these windows may be separated by a water layer, as shown in 

 r^igure 2, section A-A, thus providing for the removal of a large por- 

 tion of the infra-red radiation and at the same time for the mainte- 

 nance of the temperature of this top surface. The bottom opening is 

 provided with suitable equipment for the introduction and support of 

 the plants under observation. For convenience a metal disk may be 

 bolted over this opening, which is provided with flanges threaded for 

 the standard Mason jar. It has also been water-cooled for additional 

 convenience in temperature control. This plate is shown in a bottom 

 view in the lower left-hand corner of Figure 2. Since the frame upon 

 which the chambers are supported stands some 18 inches above the 

 floor these jars may be readily introduced from below and are sup- 

 ported from this plate by the threaded top. Thus water baths for 

 temperature control of the roots can readily be introduced surrounding 

 the jars. 



Provision is also made for the introduction of an intermediate 

 adaptor shown in the lower right-hand corner of the diagram, which 

 permits air to be bubbled through the nutrient solution in the jars 

 without escaping into the chamber above, the plants being supported in 

 cork stoppers in the usual manner. Arrangement is made so that one 

 large plant may be introduced into the chamber through a central open- 

 ing, or four smaller plants symmetrically arranged and located opposite 



