莖部第一道周皮之位置

The Site of the First Periderm in the Stem

The site of the first periderm in more than eighty dicotyledonous stems, both woody and herbaceous, were examined. 63 species have their initial phellogen in subepidermal layer; eight in primary phloem; four in epidermis; and still other one in second cortical layer. In other words, the development of the first periderm in most members takes place in shallow tissue layer. The deepest one was found to be from the primary phloem. The tissues located outside the vascular cambium may give rise to periderm. However it forms in either superficially in epidermis to second cortical layer or deep-seated in as deep as innermost cortical cells, and little is found to develop in the midway of the cortical tissue. The site of the first periderm is affected by the presence of trichomes, stomata, lenticels and the shape of the outline of stem surface. The initiation of periderm always falls behind the activation of vascular cambium.