142 University of California Publications in Agricultural Sciences [Vol.3 



but the one outlined above proved very satisfactory and much 

 simpler. 



The basic nutrient solution used throughout was Shive's three 

 salt nutrient- 4 containing the following salts in the given partial 

 molecular concentrations : 



K H 2 P0 4 0180 M. 



Ca (N0 3 ), .0052 M. 



MgS0 4 0150 M. 



The stock solution was made up to twice the strength indicated 

 above and diluted as necessary by the addition of added salt solution, 

 or distilled water, or both. 



In the case of the chlorides used, viz., calcium, magnesium and 

 potassium, normal or twice normal solutions were prepared and 

 standardized by titrating against a standard silver nitrate solution. 

 Normal solutions of magnesium and potassium sulphate were stand- 

 ardized by weighing the barium sulphate precipitate. Solutions of 

 copper, zinc, iron, and mercury salts were prepared in concentrations 

 of 1000 parts per million by weighing out the carefully dried salts. 



The final volume of solution required for the duplicate jars was 

 approximately two thousand cubic centimenters. Starting with a 

 thousand of the nutrient solution, various volumes of the standard 

 solutions were added so that when the total volume was made up to 

 two liters with distilled water, the concentrations of the various salts 

 would be those reported in the accompanying tables. 



The growing period was six weeks. The duplicate cultures were 

 grown in specially constructed mouse-proof cages each holding ninety 

 jars. The tops of the cages were open and the sides made of coarse 

 wire screening. The different parts of the cages were equally well 

 lighted, as shown by the nearly equal growth of the controls in dif- 

 ferent parts of the cages. When necessary the plants were supported 

 by cords strung across from side to side of the cages. 



The solutions were not changed during the growing period, but 

 the volumes were kept as nearly constant as possible by adding dis- 

 tilled water. There are objections to this method, as there are objec- 

 tions to the method of using water cultures at all. The growth was 

 found to be very satisfactory and compares favorably with the growth 



23 Physiol. Eesearches, no. 4 (1915), p. 174. 



24 Amer. Jour. Bot., vol. 2 (1915), p. 157. 



