•288 Ethel McLennan : 



by the air and condensing on the sides of the glass cylinders. In 

 order to prevent the air from being too moist, U-tubes containing 

 pure calcium chloride were inserted betweeen the last wash-bottle 

 and the cotton plug. 



Watering with the nutritive solutions was carried out by a siphon 

 arrangement. A glass tube bent at an angle over each pot was 

 connected by rubber tubing to a separating flask. This was tightly 

 stoppered, and the stopper coveied by a small inverted beaker to 

 prevent dust from falling on it. By raising or lowering this flash 

 the solutions flowed freely on to the pots and the quantities given 

 could be altered at will. 



The pots themselves had, glazed surfaces, and were quite nitrogen 

 free. 



Before setting up the experiment, all the glass bottles and tubing 

 were washed with the cleaning mixture, and then several times 

 with nitrogen-free water. The open ends were plugged with cotton 

 wool and sterilised, in a steam steriliser, on three successive days. 

 Ihe rubber stoppers and tubing were boiled in dilute alkali, then 

 in dilute acid, and subsequently washed with nitrogen free water. 

 Connections were made as soon as possible after removing the 

 plugs. 



The slot in the stand into wiiich the cylinders fitted was sealed 

 with putty, all the other joints were sealed with paraffin. There 

 was every indication that the connections were air-tight. 



The grains before planting were treated with a 2% formalin solu- 

 tion for 8 minutes, then washed thoroughly in nitrogen-free water. 

 By previous trial it was found that this treatment did not affect 

 the germination capacity of the seeds, and rendered them as 

 sterile as possible. 



The sand, being prepared in the manner already described, was 

 sterilised, left to cool, moistened with nitrogen-freej distilled water, 

 and the grains planted. The shades were immediately fitted into 

 place, the connections made, and the experiment commenced run- 

 ning on August 18th, 1919. It was so arranged that an equal 

 amount of illumination was received by both, pots. 



The drying tubes soon became saturated with water, and it was 

 found necessary to change them every second day. The U-tubes 

 when not in use Avere kept sterilised and plugged, so that the 

 sterility of the system was not affected by this factor. The sul- 

 phuric acid and water in the wash bottles was also changed occa- 

 sionally, so as to prevent any traces of nitrogen accumulating in 



