Fig. 5. Epidermal and transfer cell structure in wild-type pea embryos stained with Toluidine Blue in A,E,I and viewed by transmission electron microscopy in B-D,F-H,J-L. (A) Young embryo at late heart stage (50 mg seed weight) with single epidermal cell layer (ep) and underlying parenchyma cells (p). (B) Ultrastructure of the epidermal layer and parenchyma cells seen in A. (C) Morphology of outer wall of epidermal cell (upper frame in B). (D) Morphology of inner wall of epidermal cell, facing the parenchyma (lower frame in B). (E) Embryo from a 160 mg seed with single-celled transfer layer (ep) and underlying parenchyma cells (p). (F) Ultrastructure of the transfer cell layer and underlying parenchyma cells seen in E. (G,H) Morphology of (G) outer cell wall (upper frame in F), (H) inner cell wall of transfer cell (lower frame in E). (I) Embryo from a 260 mg seed showing single-celled transfer layer (arrowheads) and underlying parenchyma cells (p). (J) Ultrastructure of transfer layer and underlying parenchyma cells seen in I. (K) Higher magnification of upper frame in J showing cell wall ingrowth (arrowhead). (L) Higher magnification of lower frame in J showing branched-type plasmodesmata (arrowhead). ap, amyloplast; ep, epidermis; er, endoplasmic reticulum; m, mitochondrion; n, nucleus; p, parenchyma; v, vacuole. Scale bars: 10 µm (A), 5 µm (B), 1.25 µm (C,D), 6 µm (E,F,I), 0.4 µm (G, H), 4.5 µm (J), 0.56 µm (K, L).