Hoagland —86— Plant N utrition 



The continuation of this research in association 

 with Skoog and Broyer (1938) also produced evidence 

 that an auxin plant hormone, beta indolacetic acid, 

 could increase the magnitudes of the root pressures or 

 bleeding rates, superimposed on the cycle I have just 

 described, presumably through influencing the meta- 

 bolic activities of cells that are interrelated with active 

 accumulation or transport of salt.* 



Another mode of approach to the problem (HOAG- 

 LAND and Broyer, 1942) of the secretory-like activity 

 of root cells, which also furnishes certain further 

 suggestions concerning the question of cell permea- 

 bility, is found in the method of applying suction to 

 the cut stem of a tomato plant and thus causing 

 liquid to move through the root system under pre- 

 scribed conditions in the culture solution environ- 

 ment. This is similar to the method of Kramer 

 employed for studying water movement. Bromide 

 was again chosen for convenience as an indicator ion. 

 The plants were first subjected to an aerobic condition 

 in the culture solution and liquid was collected from 

 the cut stems. Bromide concentration rose to higher 

 values in the recovered fluid than in the external 

 solution. Then nitrogen was passed through the solu- 

 tion in one treatment, carbon dioxide in another and 

 in a third treatment the passage of air through the 

 solution was continued. With either the CO2 or N2 

 treatments there first occurred a sudden decrease in 

 the concentration of bromide present in the liquid 

 recovered from the plants. The concentration became 

 lower than that of the external solution, whereas 

 under the aerobic condition the concentrations re- 

 mained higher. Soon, however, the curve for the 

 CO2 treated plant assumed an upward trend and the 



*The writer is informed that two of the same investigators 

 met difficulty in repeating these auxin experiments at Harvard 

 University. A possible explanation of the discrepancy might 

 be that different climatic conditions caused the production of 

 plants with different potentiality of response to auxin. 



