16,6 Espino: Salt Requirements of Young Rice Plants 467 
centimeters deep). The jar was kept full of tap water so that 
the seeds were supported at about the surface of the liquid. 
Unlike wheat, this rice does not ferment rapidly when the water 
about it remains unchanged, and this fact, together with the 
large volume (about 90 liters) of water lying below the seeds, 
made it seem unnecessary to change the water during the ger- 
mination period. The germination jar stood in a greenhouse 
room, exposed to sunlight. The seedlings remained on the net 
till the shoots were from 3 to 5 centimeters long, requiring a 
period of from ten to fifteen days, depending on weather con- 
ditions, especially temperature. 
At the end of the germination period uniform and apparently 
vigorous seedlings were selected for the cultures.^^ These were 
placed in a dish of tap water, from which they were taken 
one by one, and mounted in paraffined cork stoppers of the 
form used by Shive (1915). Each stopper had six holes and 
six seedlings were held, one in each hole, by means of properly 
compressed plugs of cotton. These preparations were then put 
in place in the openings of the culture bottles, which were of 
the 250 cubic centimeter form used by Shive (1915). Card- 
board covers like the ones described by that writer (1915) were 
placed around the bottles so as to keep the interior nearly dark. 
Each bottle contained 250 cubic centimeters of the proper nutrient 
solution and the roots of the seedlings were almost entirely im- 
mersed in the liquid. The seeds were supported just beneath 
the lower surface of the stopper and were not in contact with 
the liquid. 
SOLUTIONS 
SINGLE-SALT STOCK SOLUTIONS 
In preparing the culture solutions single-salt solutions of half- 
volume molecular concentration were first prepared. The 
salts used were “Baker analyzed” monopotassium phosphate 
(KH 2 PO 4 ), calcium nitrate [Ca (NO^jg], magnesium sulphate 
(MgSO^), ammonium sulphate [(NH^),SOJ and monocalcium 
phosphate [Ca(H 2 P 04 ) 2 ].^® No attempt was made to dry the 
salts or to determine their water contents, the data on water 
" On internal differences between seedlings that might be supposed to 
be alike, see Stiles, W., On the the relation between the concentration of 
the nutrient solution and the rate of growth of plants in water culture, 
Ann. Bot. 29 (1915) 89-96. 
“ The stock solution of monocalcium phosphate was twelfth-molecular 
instead of half-molecular. 
