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 necessary 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
