Anatomical considerations related to photosynthesis in cotton (Gossypium hirsutum L.) leaves, bracts, and the capsule wall

Light and electron microscopy was used to relate histologicaland ultrastructural differences of cotton (Gossypium hirsutumL.) leaves, bracts, and capsule walls to their different photosyntheticactivities. Light microscopy revealed that the leaf thicknesswas approximately 152µm, had a well-defined internal organizationwith elongated palisade mesophyll cells and loosely packed spongymesophyll cells. In contrast, the bract was thinner (111 µm),lacked a defined palisade layer, and was largely composed ofinternal air spaces. The capsule wall was very thick (1013µm)and composed of numerous tightly packed, paren-chymatous corticalcells with little or no intercellular air space. Chloroplastswith well-defined granal stacks and extensive stroma lamellaewere observed in each of these three tissues, however, theirdensity was always greater in the palisade cells of the leafcompared to spongy mesophyll cells of the bract and the parenchymatouscells of the capsule wall. The low rates of photosynthesis inthe bracts and the capsule wall were associated with the internalorganization of these tissues. Key words: Cotton, photosynthesis, anatomy, cuticle, tissues