PLANT MORPHOGENESIS FOR SCIENTIFIC MANAGEMENT OF RANGE RESOURCES 



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STEMS and PETIOLES 



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TIME (days) 



Figure 3. — Fresh weight of total plant and individual parts as affected by addition of NaCl to growth solution. 

 Arrows indicate time of addition of each 24 meq. NaCl per liter of nutrient solution (each addition resulted 

 in increase of solution k by 1 bar). Solid circles represent control plants, and open circles represent salt- 

 treated plants. Each point is the average of 5 plants. Total NaCl added equalled 96 meg./liter, which was 

 equivalent to a final osmotic pressure of 4 bars greater than the control solution. 



that agreed with Meiri and Poljakoff-Mayber 

 (38). It became clear to us that there are two 

 extremely important considerations to be made 

 in studies of this type. (1), The environment in 

 which the leaves develop is important in deter- 

 mining how leaves respond to a given level of 

 internal stress. (2), When comparing leaves on 

 treated and nontreated plants, one must be ex- 

 tremely careful to compare the correct leaves. 

 The first leaf initiated on each plant, for ex- 

 ample, may not be physiologically similar. Dif- 

 ferences in leaf thickness between salt-treated and 

 control plants have not been found to be the same 

 by all investigators (38, 1$). We found that 

 leaves present on the plant and expanding during 

 the period of osmotic adjustment are not as thick 

 as the corresponding leaves on control plants, but 



leaves initiated subsequent to osmotic adjustment 

 are thicker than corresponding leaves from con- 

 trol plants (46). We also found that there is nor- 

 mally a greater variation in thickness within a 

 leaf and between leaves on control plants than on 

 salt-treated plants (56). The salt-treated plants 

 have smaller leaves with more uniform thickness. 

 Thus, it makes a difference what part of what 

 leaf happens to be selected for comparison. Bean 

 leaf expansion is not a simple process (10, 61), 

 and varying results among workers are likely, 

 even under controlled-environmental conditions. 

 In summary, this writer feels that the increased 

 turgor pressure and increased dry weight per unit 

 leaf area are indicative of cells that have de- 

 veloped increased rigidity in the cell walls, in 

 response to the increased -n in the leaf cells. In- 



