658 



]. van Overbeek and L. Dowding 



dark chamber. The oats are grown in the dark, interrupted only by 

 short periods of red light from a neon tube of ruby red glass. 



The Test Solution 



Solutions are prepared j^rior to cutting the sections. The stock 

 solution contains 2 per cent sucrose and 0.02 M phosphate buffer 

 (Na2HP04 and KH0PO4). Double-strength regulator solutions are 

 made so that equal parts of it can be added to the buffer to give a 

 final concentration of 1 per cent sugar and 0.01 M buffer at a pH of 

 6.2. One ml. of buffer and 1 ml. of test solution thus give the final 

 2 ml. of sohuion in ^vhich the sections are placed. 



Preparation of Beakers 



Fifty-ml. beakers are heat sterilized in paper bags, as are the watch- 

 glasses which later will serve as covers. The beakers and cover glasses 

 are stored in the bags and remain sterile for some time. The test so- 

 lutions are placed in the beakers and kept covered with the watch- 

 glasses. No special effort is made to sterilize the solutions themselves. 



UJ 



CD 



5 



Q. 

 Q- 



O 

 < 



3 CM. -~l 







0.01 



0.1 



PPM 6IBBERELLIC ACID 



I'ig. 1. Avena leaf section icsi. Tlic leal is shown as it grows oui of the basal 5 mm. 

 of the coleopiile. Duration of liic test: 48 hrs. 



