2 SMITHSONIAX MISCELLANEOUS COLLECTIONS VOL. 87 



two pieces of netting were separated by a piece of glass rod 0.5 cm 

 thick, bent to fit inside the dish. As the roots grew through the 

 mesh the two layers served to hold the plants in an upright position. 

 Flowing tap water was passed through the dish in a manner to 

 keep the upper layer of netting afloat. The plants were illuminated 

 by a 200-watt Mazda lamp placed 30 cm above the netting. Lateral 

 light was cut off by surrounding the germination net and plants with 

 black cardboard tacked to a light wooden frame. This frame was 

 raised above the table level and was large enough to provide ample 

 air circulation around the plants. When the seedlings were approxi- 

 mately 3 cm in length they were transferred to the culture solutions. 

 Each culture consisted of a single plant supported by means of cotton 

 in a small hole in a paraffined flat cork stopper which fitted into a 

 2-quart Mason jar containing the nutrient solution. Four of these 

 jars were then screwed to the under side of the bottom plate of each 

 growth chamber ; the young plants extended through the holes into 

 the chamber. 



The nutrient solution was made up of the following salts with 

 the corresponding partial volume-molecular concentrations : 



Ca (N03)2 0.005 



Mg SO4 0.002 



K H2PO4 0.002 



Mil SO4 0.0000178 



H3BO3 0.00005 



The approximate calculated concentrations of the nutrient ions in this 

 solution expressed as parts per million and milliequivalents are : 



Ppm. Millicciuivalents " 



Ca 200 10. 



Mg 49 4-0 



K 78 2.0 



NO3 620 10. 



SO4 194 4.0 



POi 190 6.0 



Mn I 0.0364 



B 0.55 0.15 



° Calculations based on milliequivalent per liter ;= — x ppm. 



at. wt. 



To this nutrient solution was added humic acid ^ containing 2.4 mg 

 iron per cc at the rate of 0.5 cc per liter of nutrient solution. The 



^ The humic acid used in these experiments was supplied by Dr. Dean Burk 

 of the Fixed Nitrogen Research Laboratory, United States Department of 

 Agriculture. 



