T. C. Broyer 



223 



Figure 19. Effects of differential gas treatments on the rate 

 of exudation by decapitated tomato plants. Tomato plants grew 

 with aeration, in a culture solution of the following composi- 

 tion: KNO s , 0.0025M; Ca(N0 3 ) 2 , 0.0025 M; MgS0 4 , 0.001M; 

 KH 2 P0 4 , 0.0005 M; F e as i ron tartrate (1 ml. of 0.5 per cent 

 solution per liter of culture solution). Micronutrients as re- 

 quired. Growth period, 47 days. Experimental culture solution, 

 KBr, 5 milliequivalents per liter. Gases were continuously 

 passed through the solutions. All roots were aerated until 6 

 p. m. Differential gas treatments of air, N 2 , and C0 2 were then 

 applied. Suction equal to 740 mm. Hg was continuously applied 

 (except during observations on volume of exudate and during 

 removal of increments of exuded fluid) throughout the experi- 

 ment. At the termination of the experiment the abilities of the 

 plants to develop an exudation pressure (as a measure of the 

 state of the root systems) were noted. The following results 

 were obtained: aerated cultures, appreciable and maintained 

 exudation pressure; N 2 -treated cultures, a weak yet maintained 

 pressure; CGytreated cultures, no exudation pressure over an 

 extended interval of time. The roots in the CGytreated culture 

 were flaccid at the termination of suction exudation. 



