34 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS 



B. Make another nutrient solution (No. 2) like No. 1, but without iron ; 

 another (No. 3) containing the same ingredients as No. 1, except the cal- 

 cium nitrate, for which one gram of calcium sulphate is to be substi- 

 tuted; and another (No. 4) like No. 1, except that acid sodium phosphate 

 is to be substituted for the acid potassium phosphate. 



C. Place in each jar a vigorous young wheat seedling with only its roots 

 submerged, or a cutting of Tradescantia. Cover each jar with a piece of 

 pasteboard wrapped around the glass so as to exclude light from the 

 solution and put all the jars in a warm place but not in full sunlight. 

 Change the nutrient solution every week and continue the culture for 

 four or five weeks. If the roots seem dirty and slimy, allow the plants 

 to stand for a day or two at a time with the roots in distilled water or 

 a weak solution of calcium sulphate. 



D. At the end of the period sketch all the plants and label as follows : 



1. Culture in full nutrient solution. 



2. Culture without iron. 



3. Culture without nitrogen. 



4. Culture without potassium. 



What conclusions can you draw from the experiment ? 

 •Refeeences. Detmer-Moor, 9 ; Pfeffer-Ewart, 31, I ; Peirce, 32. 



EXPERIMENT XVI 



Effect of diminished temperature on absorption of water by roots. 



A. Transplant a tobacco seedling about four inches high into rich earth 

 contained in a narrow, tall beaker or very large test tube (not less 

 than 1^ inch in diameter and six inches high). 



B. "When the plant has begun to grow again freely in a warm, sunny room, 

 insert a chemical thermometer into the earth ; this can best be done by 

 making a hole with a sharp, round stick, pushed nearly to the bottom of 

 the tube, and then putting the thermometer in the place of the stick. 

 Water the plant well, and then set the tube in a jar of pounded ice which 

 reaches nearly to the top of the tube. Note the temperature of the earth 

 just before placing it in the ice. Cover the ice with cotton batting or a 

 piece of flannel so that the stem and leaves of the plant will not be 

 chilled by the proximity of the ice. 



C. Observe whether the leaves of the seedling wilt, and if so, at what 

 temperature the wilting begins. 



D. Finally, remove the tube from the ice and place it in warm water 

 (about 80° F. or 27° C). Observe the effect and note the temperature 

 at which the plant, if wilted, begins to revive. 



