The primary stem of Q. alba and Q. rubra shows 2 distinct initial groups, one for the dermatogen and a second (subterminal) common to both periblem and plerome. Distinct cauline strands may be distinguished in the primary tissues of the epicotyl only at any early stage of seedling development; such strands apparently take their origin just beneath the initial regions and from the marginal cells of the plerome. With the appearance of leaves or leaf-like appendages at the stem tip, the vascular elements of these members become the dominant bundles of the primary cylinder. The tissues of the leaf appear to originate from 2 initials: one for the epidermis, the 2nd for the parenchyma and the bundles. The procambial strands of the foliar organs originate in the bases of the leaf pri-mordia. Differentiation of these strands progresses from the point of origin both basipetally and acro-petally. The first thickening of xylem elements occurs in the procambial tissue in this region. Both species examined furnish evidence of variable nodal structure, the character of the node being largely determined by the nature of the developing foliar organs.