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Gossypium hirsutum L. (upland cotton) and G. barbadense L. (Pima cotton) are two of the most important fibre producing cotton species in cultivation. When grown side-by-side in the field, G. hirsutum has higher photosynthetic and transpiration rates (Lu et al., 1997. Australian Journal of Plant Physiology 24: 693‐700). The present study was undertaken to determine if the diAerences in physiology can be explained by leaf and canopy morphology and anatomy. Scanning electron microscopy was used to compare the leaf anatomy of field-grown upland (‘Delta’ and ‘Pine Land 50’) and Pima (‘S6’) cotton. Compared to G. hirsutum, mature leaves of G. barbadense are larger and thinner, with a thinner palisade layer. G. barbadense leaves show significant cupping or curling which allows for a more even absorption of insolation over the course of the day and much more light penetration into the canopy. Although G. barbadense leaves have a 70‐78% higher stomatal density on both the abaxial and the adaxial surfaces, its stomates are only one third the size of those of G. hirsutum. This results in G. barbadense having only about 60% of the stomatal surface area per leaf surface area compared to G. hirsutum. These results are indicative of the anatomical and physiological diAerences that may limit the yield potential of G. barbadense in certain growing environments. # 2000 Annals of Botany Company |
