TORREYA 



Vol. 10 



April, 1910 



No. 4 



A PLANT-CASE FOR THE CONTROL OF 

 RELATIVE HUMIDITY 



By W, T, BoviE 



In connection with some work on the non-available water in 

 soils the writer has devised a plant-case in which plants can be 

 grown under conditions of constant humidity. The apparatus 

 has given excellent satisfaction, not only in its efficiency for con- 

 trolling humidity, but also because it has made it possible to 

 determine, within a reasonable degree of accuracy, the time of 

 death of the plants. This is a necessity in non-available water 

 determinations. The relative humidity is controlled by forcing a 

 current of dried air into the plant-case by means of an air pump, 

 at a rate necessary to balance the moisture given off by the plants. 

 It is often desirable to control humidity conditions when working 

 with plants ; and as far as known to the writer the only published 

 description of a humidity balance is that of a case devised by 

 Gregaire and Hendrick.* This publication has not been acces- 

 sible to me. 



The plant-case is a cubical box, two feet on a side. The top 

 and four sides are made of plate glass, one-fourth of an inch 

 thick. Any kind of glass will do provided it be free from 

 irregularities which might refract the light-rays, like a lens. 



The frame of the case is made of wooden pieces fitted together 

 with screws, and so arranged as to hold the glass sides as a 

 window pane is held in its sash. All of the glass is set in 

 asphalt. Asphalt is also used to close the joints where the 

 several pieces of the frame are fastened together. The front of 

 the case contains a door, which is held, by means of twelve 



* Reported by A. Petermann (Bui. Inst. Chim. et Bact. Gembloux, 70: 22-3. 

 1901). See Exp. Sta. Rec. 13: 1018. 1901-02. 

 [No. 3, Vol, 10, of TOKREYA, comprising pages 52-76, was issued March 31, 1910.] 



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