332 



TEXTBOOK OF BOTANY 



Fig. 139. A convenient method of repeatedly adding a culture solution to plants 

 potted in gravel. Each bucket contains a prepared solution and is connected to a 

 pot by means of a rubber hose. At intervals the bucket is hung on the suspended 

 hook above the pot until the solution flows into the gravel. It is then returned to 

 the shelf below the pot and the solution drains from the gravel into the bucket. 

 Photo by J. D. Sayre, Ohio Agricultural Experiment Station. 



REFERENCES 



American Potash Institute. Potasli Deficiency Symptoms. 1937. In this publi- 

 cation potassium deficiency effects in many kinds of plants are illustrated 

 in color. 



Anion, D. I., and P. R. Stout. The essentiality of certain elements in minute 

 quantity for plants, with special reference to copper. Plant Physiol. 14:371- 

 375. 1939. 



Chilean Nitrate Educational Bureau. Bibliography of references to the litera- 

 ture on the minor elements. 1936. 



Hoagland, D. R., and D. I. Arnon. The water-culture method for growing 

 plants without soil. Calif. Sta. Circ. 347. 1938. 



Laurie, Alex. Soilless Culture Simplified. McGraw-Hill Book Company, Inc. 

 1940. 



McMurtrey, J. E., Jr. Distinctive plant symptoms caused by deficiency of 

 any one of the chemical elements essential for normal development. Bot. 

 Rev. 4:183-203. 1938. 



