Origanum dictamnus. Ultrastructure of mesophyll cells of winter leaf (A) and summer leaf (B). In winter leaf, chloroplasts (cp) bear grana (g) with a few thylakoids and occasionally individual starch grains (sg). Vacuoles (v) are filled with fine-granular phenolics. In summer leaf, chloroplasts contain many multi-thylakoid grana and numerous starch grains. Vacuoles are devoid of phenolics. Bars in μm.