Therefore the water potential gradient within the xylem is essentially a

Therefore the water potential gradient within the

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Stomata: Major Pathways for Water Loss o About 95% of the water a plant loses escapes through stomata, although these pores account for only 1-2% of the external leaf surface o The waxy cuticle limits water loss through the remaining surface of the leaf o Each stoma is flanked by a pair of guard cells Guard cells control the diameter of the stoma by changing shape, thereby widening or narrowing the gap between the guard cell pair Under the same environmental conditions, the amount of water lost by a leaf depends largely on the number of stomata and the average size of their pores o The stomatal density of a leaf is under both genetic and environmental control E.g. as a result of evolution by natural selection, desert plants are genetically programmed to have lower stomatal densities than do march plants o Stomatal density, however, is a developmentally plastic feature of many plants High light exposures and low CO 2 levels during leaf development lead to increased density in many species By measuring the stomatal density of leaf fossil, scientists have gained insight into the levels of atmospheric CO 2 in past climates A recent British survey found that stomatal density of many woodland species has decreased since 1927, when a similar survey way made
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  • Spring '08
  • ALAIE
  • Plants, phloem, Xylem

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