EFFECT OF TEMPERATURE 59 



enclosing the plant and fulfilling these conditions, had to 

 be devised. It will be noticed that these investigations 

 involve two opposite sets of requirements — namely, in the 

 one case a definite lowering of the temperature of the 

 chamber below, and in the other a definite raising of it 

 above, the temperature of the environment. 



The plant-chamber consists of a base-board with a 

 rectangular cover. This cover is made of a light wooden 

 framework, the sides being closed with sheets of mica. 

 The advantage of mica is its lightness, unbreakableness, 

 non-conductivity, and transparency. Transparency is 

 necessary because in darkness the sensitiveness of a plant 

 undergoes variation. The base-board consists of two 

 halves, with a small circular opening in the middle. When 

 these two halves of the base-board are slipped over the top 

 of the flower-pot they form one piece, fixed together by 

 means of suitable clasps. The base-board rests on the 

 flower-pot and the main stem of the plant passes through the 

 circular opening. The base-board thus forms the floor of 

 the thermal chamber. There are grooves cut in the base- 

 board for the reception of the wooden framework. The plant 

 is thus enclosed except on the top. After making the neces- 

 sary thread-connections of the lever with the responding leaf, 

 the top is closed by means of two sliding-pieces of mica, with 

 slits for the passage of the thread. There are two side-tubes, 

 one near the top and the other near the base, for the passage 

 in and out of a stream of cold air, when the temperature of 

 the chamber is to be reduced. When the temperature is to 

 be raised, an electrical heating arrangement is employed. 



The requirements of cooling are, first, a weighted air- 

 bag, provided with a stop-cock ; and second, a coiled copper- 

 pipe placed in an ice-box. By means of indiarubber tubing, 

 connections are made, first, between the stop-cock of the 

 air-bag and one end of the copper pipe ; and, second, between 

 the other end of the copper pipe and the upper tube of the 

 thermal chamber. Thus by more or less opening the stop- 

 cock of the air-bag a stream of cooled air is made to circulate 



