792 



A. S. Cxifts 



Because in the use of regulators as herbicides one is dealing with 

 toxic compounds, loinudation should be aimed at bringing about 

 wetting of the cuticle, ordered uptake into the mesophyll, controlled 

 concentration to a\oid injury to sieve tubes, and accumulation to 

 toxic levels in the roots. Balanced solubility in lipoid and aqueous 

 phases is essential, and proper partitioning is required. 



If regulators are absorbed via an aqueous route, there must be 

 pores from the interior of the leaf to the outer surface which under 

 saturated conditions are water filled. Electron microscope views of 

 the cuticle and of cellulose indicate that such pores exist (9, 11). The 

 aqueous medium in the leaf is undoubtedly a continuum with the 

 saturation of the surface dependent upon the water balance of the 



Fig. 1. Apoplastic iiioxciuciii ol .niniiol in l)tan leaf as sliown by the dark wedge- 

 sliapcd patlcrn ol an aiiloiadiograin. Symplastic movement also is shown by label- 

 ing of stem, roots, and iiifoiialc leal. nosa'j;c, ]'2') ^ug, as a drop at base of primary 

 leaf. Treatment period 8 hrs. 



