ANATOMICAL CONSIDERATIONS RELATED TO PHOTOSYNTHESIS IN COTTON (GOSSYPIUM-HIRSUTUM L) LEAVES, BRACTS, AND THE CAPSULE WALL

Light and electron microscopy was used to relate histological and ultrastructural differences of cotton (Gossypium hirsutum L.) leaves, bracts, and capsule walls to their different photosynthetic activities. Light microscopy revealed that the leaf thickness was approximately 152 mu m, had a well-defined internal organization with elongated palisade mesophyll cells and loosely packed spongy mesophyll cells. In contrast, the bract was thinner (111 mu m), lacked a defined palisade layer, and was largely composed of internal air spaces. The capsule wall was very thick (1013 mu m) and composed of numerous tightly packed, parenchymatous cortical cells with little or no intercellular air space. Chloroplasts with well-defined granal stacks and extensive stroma lamellae were observed in each of these three tissues, however, their density was always greater in the palisade cells of the leaf compared to spongy mesophyll cells of the bract and the parenchymatous cells of the capsule wall. The low rates of photosynthesis in the bracts and the capsule wall were associated with the internal organization of these tissues.