;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 tlie stopper coveied by a small inverted beaker to 

 prevent dust from falling on it. B\ 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 Avater. The open ends were plugged with cotton 

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

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

 in dilute acid, and subsequently Avashed with nitrogen free Avater. 

 Connections AA-ere made as soon as possible after removing the 

 jplugs. 



The slot in the stand into which the cylinders fitted Avas sealed 

 Avith putty, all the other joints Avere sealed Avith paraffin. There 

 Avas every indication that the connections were air-tight. 



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

 tion for 8 minutes, then Avashed thoroughly in nitrogen-free Avater. 

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

 the germination capacity of the seeds, and rendered them as 

 sterile as possible. 



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

 sterilised, left to cool, moistened with nitrogen-free] distilled Avater, 

 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 Avas so arranged that an equal 

 amount of illumination Avas receiA^ed by lx)th. pots. 



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

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

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

 sterility of the system Avas not affected by this factor. Ihe sul- 

 phuric acid and water in the Avash bottles Avas also changed occa- 

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



