TRANSLOCATION OF CARBOHYDRATES IN MAIZE

(1) The pith of maize shows a changing sugar content with changing sugar movement in the phloem which would not be predicted from our present picture of the morphology of the maize bundle. (2) By all tests of changing concentration, sucrose is the important carbohydrate of translocation in maize. Interconversion of the several sugars is too rapid, however, to permit a final conclusion. (3) An hypothesis of translocation in maize must not only account for movement against an osmotic gradient, but against gradients of each of the substances which might possibly be translocated. Such secretory translocation certainly occurs between the leaf mesophyll and the phloem and probably along the phloem itself. (4) Translocation in maize is polarized, out of the leaf, out of the xylem and toward the developing fruit. Polarized translocation out of the leaf is established during the later stages of tissue differentiation. Polarized translocation toward the fruit is established in the early phases of embryo development and does not develop in the absence of pollination.