EXERCISE X. 



PLANT GROWTH AFFECTED BY THE ELEMENTS, NITROGEN, POTAS- 

 SIUM AND PHOSPHORUS. 



*Supplies for one Student. Detmer-Moor culture solution. A complete culture solution prepared u follows: 

 2,880 cubic centimeters of distilled water, 7 grams of potassium nitrate, 1.5 grams magnesium sulphate, 1.5 grams 

 sodium chloride, 1.5 grams neutral potassium phosphate, enough calcium sulphate so that a small quantity will 

 remain in suspension when the solution is shaken. 



A culture solution without potassium prepared as follows: 2880 cc. distilled water, 7 grams of calcium nitrate, 

 1.5 grams magnesium sulphate, 1.5 grams of neutral sodium phosphate. 



A solution without nitrogen prepared as follows : Substitute potassium sulphate for potassium nitrate in the 

 complete solution. 



A solution without phosphorus prepared as follows: 1000 cc. of distilled water, 0.5 gram of potassium, nitrate, 

 0.5 gram of neutral potassium sulphate, 0.5 gram of calcium nitrate, 0.5 gram of magnesium nitrate. 



Germinating corn, barley, or wheat; four opaque water culture jars with thin two-hole corks to fit; absorb- 

 ent cotton ; ferric chloride solution. 



DIRECTIONS. Label and number the jars 1, 2, 3, and 4. Fill jar No. 1 with the com- 

 plete culture solution, jar No. 2 with the culture solution lacking potassium, jar No. 3 with 

 the culture solution lacking nitrogen, and jar No. 4 with the solution lacking phosphorus. The 

 jars should be filled to within about J4" of the cork. Add two drops of ferric chloride solution 

 to each jar of culture solution. Ferric chloride contains iron which is important in producing 

 and maintaining chlorophyll, the green coloring matter of plants. The presence of this sub- 

 stance also hinders the growth of moulds which are apt to attack the roots of plants growing 

 in culture Solutions. 



Select seedlings having roots several centimeters in length. Remove them carefully from 

 the germinator and wash away any excess material from the roots. Fix one or two of the 

 best seedlings in each cork by means of absorbent cotton in such a way that the roots will 

 extend down into the solutions in the culture jars. Air should be bubbled through the solu- 

 tions every 4 or 5 days. 



1. Observe the plants daily for about two weeks. At the close of the period, describe 

 the growth, color, and leafiness of the plants. 



.2. It is sometimes said that nitrogen or some other element of plant food has become a 

 limiting factor in plant growth or crop production. What is meant by such a statement? 



Reference: "Soils and Soil Fertility." Whitson and Walster. Article 99, p. 71-73. 



'Note: It will be well to have the laboratory section wsrk as a (roup on this exercise. Each student sheuld, 

 however, make independent observations and records. 



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