The Leaves

Structure and function. The diagrams at the top of this page and the next represent sections of a leal blade as seen under a microscope. The blade is bounded by an upper and lower epidermis, both covered by an impervious cuticle. Many minute pores, the stomata, each surrounded by two sausage-shaped guard ceils, are present, particularly tn the lower epidermis. The stomata are open during the day and allow gaseous diffusion between the external atmosphere and the intercellular spaces of the mesophyll. The mesophyll consists of thin-walled cells containing many minute green discoid structures, the chioroplasts. Also present is a network of veins, small vascular strands of xylem and phloem which are in connection with that of the stem via the leaf stalk.

In light, photosynthesis occurs in the chioroplasts. This is a complex series of reactions in which waler supplied from the soil and carbon dioxide from the atmosphere are combined to form carbohydrates. In soluble form this elaborated food material is transported away from the leaf in the phloem.

As the stomata are open during the day a great amount of water evaporates from the leaf. This transpiration sob-stomatal chamber cMoroplast epidermis ouard cell

sob-stomatal chamber cMoroplast

0 0

Post a comment