SOLUTION AND SAND CULTURES 431 



H3BO3), manganese (as MnS04 • 4H2O) and zinc (as ZnS04 • yH^O) 

 are also added. A number of species of agricultural plants have been found 

 to give excellent growth w^hen supplied with this solution in either solution 

 or sand cultures. 



Hoagland and Snyder (1933) recommend the following stock solution: 

 Ca(N03)2 0.821 g., KNO3 0.506 g., KH2PO4 0.136 g., I\lgS04 0.120 g., 

 water i liter, and ferric tartrate i cc. of a 0.5 per cent solution repeated at 

 intervals. To this they suggest the addition of an "A-Z" solution which is a 

 supplementary solution containing small quantities of a number of the elements 

 known to be necessary for plants, or which possibly may be necessary. The 

 principal supplementary solution used by these investigators was prepared as 

 follows : 



LiCl 0.5 g. MnCl2-4H20 7-o g- 



CuSOi-fHsO i.o NiS04-6H20 i.o 



ZnS04 1.0 Co(N03)2-6H20 1.0 



H3BO3 ii.o Ti02 1.0 



Al2(S04)3 I.O KI 0.5 



SnCl2-2H20 0.5 KBr 0.5 



Water 18 liters 



This solution contains ten elements which have not usually been provided 

 in solution cultures. One cubic centimeter of this solution is added to one 

 liter of stock solution described above. 



Such supplementary solutions can also be used with other stock solutions. 

 Most of the species of plants which have been tried have shown better develop- 

 ment when the conventional solutions in which they were grown were forti- 

 fied by the addition of a small quantity of such a supplementary solution than 

 when they were not (Schropp and Scharrer, 1933, and others), although it 

 has by no means been demonstrated that all of the elements present in such 

 solutions are necessary. 



In solution culture experiments the prepared solution is transferred to a 

 suitable vessel the size and shape of which depends upon the type of investiga- 

 tion and size of the plants to be studied. IVIason jars, crocks of various sizes, 

 and shallow trays are M'idely used in solution culture investigations. Seedling 

 plants of the species to be studied are then fastened in place in such a way 

 that the root systems are immersed in the solution. 



Many precautions must be observed if reliable results are to be obtained 

 with solution cultures. Only a few of the most important of these can be 

 summarized in this discussion : ( i ) All of the solutions used in any series 

 must have essentially the same osmotic pressure (why?). In general only 



