Some of the unique features regarding plant respiration are:<\/p>\r\n\r\n
In a study reported in\u00a0 <\/span>Nature<\/strong>,\u00a0<\/span>411<\/strong>:287, 17 May 2001) by Gregory Retallack\u00a0 it was said that the fossil leaves of the ginkgo and its relatives showed high stomatal indices\u00a0\u00a0<\/span><\/strong>late in the Permian period (275\u2013290 million years ago) and again in the Pleistocene epoch (1\u20138 million years ago). Geological evidence show that both these periods are known for low levels of atmospheric CO<\/span>2<\/span><\/sub> and ice ages. On the contrary\u00a0<\/span> during the Cretaceous period, a time of high CO2<\/span><\/sub>\u00a0<\/span>levels and warm climate , stomatal indices were\u00a0 reported to be low.<\/span><\/p>\r\n These studies support the role of\u00a0 carbon dioxide as a greenhouse gas and its contribution in global warming.<\/p>\r\n\r\nGaseous Exchange in Roots and Stems<\/h1>\r\nMature woody stems and roots are covered by dead cells called Cork cells that are filled with a waxy, air and water proof substance called Suberin which makes the roots and stems impervious to water and air . But\u00a0 the cork of both mature roots and woody stems\u00a0 contain non suberized\u00a0 pores called <\/span>lenticels<\/strong>. These enable the gaseous exchange in roots and stem.<\/span>\r\n\r\nThe stems of many annual plants are green and they take part in photosynthesis . In such stems the stomata are used for gas exchange rather than the lenticels.\r\n\r\nIn Cacti and succulents have a different adaptation . Their\u00a0stomata remain closed during in order to prevent moisture loss in the hot, dry environments .However their stomata open at night instead, and the CO2<\/span><\/sub> is stored as an acid in large sacs (called vacuoles) within their cells until it\u2019s needed for photosynthesis . These fluid-filled vacuoles create the thick, fleshy leaves and stems that are characteristic of these plants.\u00a0<\/span>\r\n