Fig. 2

Transmission electron micrographs of transverse sections of celery collenchyma cells at four stages of development. a, Stage 1; b, Stage 2; c, Stage 3; d, Stage 4. The insets are low magnification images of the collenchyma cells and the rectangles show thickened walls at the cell corners used for the high magnification images in the main panels. These high magnification images show the polylamellate structure of the collenchyma cell walls. Scale bars= 500 nm (main panel) and 2 μm (insets)