Transpiration and Water Movement 



105 



effects, for one thing, perhaps, a rapid distribution of 

 absorbed mineral nutrients. 



On the other hand there is (2) a more gradual movement 

 by diffusion of soluble organic materials, or " elaborated" 

 foods, along the paths provided by the plasmatically con- 

 nected sieve tubes (Fig. 33), from which general paths 



X 



P 



FIG. 33. Longitudinal section of a bundle similar to the preceding. 



[After Curtis.] 



organic substances pass, also by diffusion, into all cells 

 where growth and differentiation are proceeding. At 

 certain seasons, in many plants during the spring, the 

 movement of organic material in the xylem part of the 

 bundles is common. Usually, however, the distinction 

 may be made that the dead vessels or xylem elements 

 conduct a liquid which is more nearly the nutrient solu- 

 tion absorbed from the soil, whereas the sieve-tube part 

 of the bundle is primarily the path of diffusion for organic 

 materials. All cells of the body- -parenchyma, cortex, 



