Mineral Nutrients 167 



the water lost by transpiration. If the cultures are continued 

 longer than two weeks, renew the solutions. When necessary, 

 support the plants by the wire standard and ring (Fig. 44). Close 

 the experiment within four weeks, measuring tops, weighing roots 

 and tops separately, taking notes on general appearance, tabulat- 

 ing results, and representing graphically the green weight of tops 

 and of the whole plant. 



Corrosion by roots. Place the polished marble plates provided 

 in the small germinating plats (cigar boxes 2 inches deep answer- 

 ing well), cover with 2 inches of sand, sow seed of squash and bean, 

 and maintain under conditions favorable for growth. When the 

 seedlings have grown vigorously to a height of 5 or 6 inches, exam- 

 ine the marble plates for etched tracings. 



Determination of acid excretion by roots. When the two addi- 

 tional tumblers employed in a preceding experiment with nutrient 

 solution afford vigorous seedlings, set up the following experiment : 

 Boil one liter of tap water in a flask, cool, and aerate, make slightly 

 alkaline with potassium hydrate, and add a few drops of phenol- 

 phthalein to give distinct pink color. With this solution fill four 

 tumblers, two of which are to be covered with paraffined paper as 

 controls ; to the other two transfer the covers and seedling peas 

 above indicated. Place both sets under similar conditions, and 

 after 24 hours note and compare the color in the two cases. If the 

 pink color has disappeared, the solution has become acid. In 

 that case pour the contents of one tumbler into an evaporating 

 dish, and bring to a boil. If the color reappears promptly, it in- 

 dicates carbonic acid. 



REFERENCES 



BENECKE, W. Die von der Cronesche Nahrsalzlosung. Zeitsch. 



Bot. 1 : 235-252. 

 BREAZEALE, J. F. Effect of the Concentration of the Nutrient 



Solution upon Wheat Cultures. Science, N. S. 22 : 146- 



149, 1905. 

 CAMERON, F. K., and BELL, J. M. The Mineral Constituents of 



