122 AisnsruAL report Smithsonian institution, 1951 



conductance bridge especially designed for the purpose. Absorption 

 of various nitrates, chlorides, and sulfates of potassium, calcium, and 

 magnesium was studied. The results indicate that there is a marked 

 reduction in salt uptake when the plants are treated with NH4-2,4-D 

 and that this reduction is concomitant with a reduction in growth and 

 does not precede it. With all salts except potassium and calcium 

 nitrates, the reduced uptake does not appear until 24 to 48 hours after 

 application of the regulator. In the case of potassium and calcium 

 nitrate the effect begins within the first 24 hours. 



It was also found that water absorption was markedly reduced when 

 either the bud or primary leaf of bean was treated with NH4-2,4-D, 

 the greater reduction occurring when the leaf was treated. The re- 

 duction was not related to an effect on a root mechanism since it oc- 

 curred on excised shoots to the same magnitude as in whole plants. A 

 rapid weighing technic showed that the loss of water from the plant 

 treated with NH4-2,4-D was considerably less than for plants not so 

 treated, indicating that transpiration is greatly reduced by treatment 

 with 2,4-D. 



During the year a contract was assigned to the division by the 

 Atomic Energy Commission to study the effect of radiation on the 

 growth and development of plants. A contract renewal was awarded 

 by the Biological Department, Chemical Corps, Camp Detrick, Md., 

 to continue physiological studies of the effect of growth regulators on 

 plants. 



RespectfuUj^ submitted. 



L. B. Aldrich, Director. 



Dr. A. Wetmore, 



Secretary^ Smithsonian Institution. 



