432 



The device cost only $50, but it required some supervision, as it was made 

 too large throughout. At the present time it would be cheaper to pur- 

 chase the standardized turn-table direct from the Plant World, all ready 

 to use, but of a smaller size. 



C. Special Methods. 



Special methods and special equipment will be discussed here. The 

 larvae studied were placed in corrugated papers with celluloid covers and 

 backed up by small pieces of wood, after the manner used by Mr. Glenn. 

 In fact, we secured some of his observation cases and merely selected a 

 container which would hold them, modifying them only slightly (Fig. 

 34). The sticks used were 4 inches (10 cm) long and one inch (2.5 cm) 

 wide. The celluloid covers were supported by wood 2-3.5 mm thick, 

 allowing a space between the celluloid and the wood back. We mounted 

 the back of the piece of wood in order to make two of them approach a 

 cylindrical form. Two were commonly placed face to face, and when 

 only one was used it was provided with a dummy front piece of wood 

 without the pasteboard. The bottles used for most of the experiments 

 were of 250 cc capacity with an inside diameter of about 2^4 inches (56 

 mm) and an outside diameter of a little less than 2J<^ inches (61 mm). A 

 pair of sticks with their larvae were dropped into a bottle and the two 

 taken together made an elliptical cylinder with a diameter of one inch by 

 % inch. Each one of these bottles was provided with a two-hole rubber 

 stopper. Air was introduced through a tube inserted into one of these 

 holes in the rubber stopper, the tube ending at the lower edge of the 

 stopper, and air left the bottle through a tube extending to the bottom. 

 Thus the tube extending to the bottom tended to push the elliptical 

 cylinder to one side and it rested immediately beneath the incoming air 

 which flowed down over the larvae container to the bottom and out. 

 Leaving the bottle, the air was conducted through a small tube into 

 another bottle of the same kind, from which the bottom had been removed 

 by a skilled glass-worker. This bottle rested over a Livingston porous 

 cup atmometer, which is a little more than one inch in diameter and just 

 a little larger than the bottle used as a larvae-conta'ner. Thus the 

 apparatus for experimentation was so arranged that the air flowed 

 through the bottle and then over the atmometer at approximately the 

 same rate at which the evaporation was measured. These containers were 

 mounted on pieces of board about 3 inches by 6 inches (7.5 cm by 15 cm). 

 See Fig. 34. The bottle containing the larvae rested on the board and 

 was held in place by three or four slender nails driven into the board. The 

 atmometer, with the recording attachment at its lower end, was sup- 

 ported on a piece of soft aluminum tubing, 14 inch inside diameter, bent 

 into the form of an elbow, inserted through a flat stopper, a channel 

 being cut in the lower side so that one arm of the aluminum tubing rested 

 in this, flush with the underside. This was nailed to the end of the board 

 opposite to that to which the bottle was placed. Above this three corks 

 13^ inch (3.7 cm) by approximately one inch (2J^ cm) in diameter were 



