194 



TRANSLOCATION IN PLANTS 



Table 21.- 



-Radial Distribution of Sugars and Nitrogenous 

 Compounds in the Bark 

 Milligrams per 100 g. water 

 (Frorn Maskell and Mason) 



Inner 

 fraction 



846.3 

 390,0 

 456.3 

 329.0 

 39.3 

 88.0 



Total nitrogen 



Protein nitrogen 



Total crystalloid nitrogen 



Asparagine nitrogen 



Amino-acid nitrogen 



Residual nitrogen + / . . . 

 Nitrate nitrogen ) 



Sucrose 



Reducing sugars 



Total sugars 



2,565.0 

 3,082.0 

 5,647.0 



bark following various treatments are to be ascribed 

 chiefly to changes in sucrose content of this inner region. 

 These changes were normal changes with time as well as 

 those induced by defoliation or ringing. It was found that 

 the radial gradient of sucrose in particular was altered by 

 defoliation or ringing. Defoliation resulting in a decrease 

 in transport of sugar caused a marked falling off in total 

 sucrose and the sucrose gradient. Ringing below the 

 tested region so as to prevent removal of sugar increased 

 the concentration of sucrose as well as the radial gradient. 

 When conditions were such as to bring about movement 

 of sugar from leaf to bark, bark to leaf, bark to boll, bark 

 to wood, or one part of the stem to another part, above or 

 below, they always found diffusion gradients for sucrose 

 in the respective tissues to lead in the proper direction; 

 and, furthermore, where rates were estimated, these rates 

 showed a high correlation with concentration gradients. 



Their evidence strongly supports their conclusion that 

 sucrose is the translocation sugar and that the rate and 

 direction of translocation are determined by diffusion 

 gradients. The observed rates of movement through the 

 phloem, however, would give a diffusion constant for 



