Herbaceous Dicot Vine: P-protein Plugs In Phloem Cucurbita - Long Section: Cucurbita Stem Magnification: 400x The Epidermis Is Usually Single Layered With An Outer Cuticle And Multicellular Trichomes. Phloem Consists Of Large Clear Sieve Tubes With Pitted Cell Walls And Sieve Plates And Small Narrow Green Stained Companion Cells. Many Sieve Plates Have Deposits Of A Mucoid P-protein That Forms As Part Of The Trauma Response In Injured Phloem. Between The Xylem And Phloem Are A Few Regularly Arranged Layers Of Elongated Cambium Cells. Photo