' 



ordinary sealing wax, applied hot and sealed down to 

 the tin and glass surfaces by subsequent oareful appli- 

 cation of the flame of a gas-blowpipe. Connections with 

 the outside, for purposes of control of the soil atmo- 

 sphere, are provided by two tubes; one of glass, in- 

 serted by the side of the water-tube through one of 

 the holes in the top; the other of lead, soldered into 

 the side of the tin can toward the bottom. The glass 

 tube at the top is sealed in with sealing-wax in the 

 same way as is the water-supply tube. The soldered 

 joint between the lead tube and the side of the tin 

 can is made air-tight. The general arrangement of the 

 can, plant, and connection tube is shown in figure 1. 



The seal around the plant stem presented con- 

 siderable difficulty. The simple seal of wax or graft- 

 ing-wax, as used by previous investigators, will not 

 last more than a few days without cracking and allowing 

 leakage. It is necessary that the seal remain air- 

 tight and yet permit the slow enlargement of the 

 stem which accompanies the growth of the plant. It 

 is obvious, also, that the seal must not require con- 

 tact of the stem with any substance which will be in- 

 jurious to it. Lany devices were tried and discarded. 

 Split rubber stoppers, or rubber tissue wrapped about 

 the stem were found to be unsatisfactory because of 

 interference with enlargement of the stem and consequent 



