STRUCTURE AND DEVELOPMENT OF STOMATA

Structure and Development.of Stomata.—Stomata are slit-like openings in the epidermis of leaves or young green stems surrounded 

—Photomicrograph of a transverse section of a bifaciai leaf of Eucalyptus globulus showing epidermis (ep.), palisade parenchyma (pep.), toward both surfaces, spongy parenchyma (s.p.), vein (r), and oil reservoir (o.r.) lined with secretory epithelium. (Highiy magnified.) 

On all dorsoventral leaves, the stomata arise more abundantly on the lower epidermis, less abundantly on the upper. Exceptions to this rule are due to the peculiar readaptation of the leaf to its surroundings. Thus, in the reversed types of leaves (twisted in a half circle) the stomata, formerly on the lower surface, have migrated to the upper surface which now has become the physiological lower surface. 

In Umbrophytic (shade) plants the stomata are either wholly on the lower surface or partly so with a number on the upper surface. Where the plants are Mesophytic and exposed to dense sunlight and leaves remain dorsoventral, the stomata are on the lower surface these stomata are large, if the surroundings are damp. If such plants live in dry soil and dry air, the stomata are of small size and numerous if they dwell in dry soil in hot surroundings and dense light they are very small and frequently sunk. If the plants are Xerophytic and the leaves dorsoventral, the stomata are quite abundant, small, with narrow slit, and depressed below the level of the epidermis. 

while at first flat and inoperative, soon become bulged and crescent-shaped. This mode of development is seen in Squill, Hyacinth, Daffodil, Sambucus, Silene, etc. 

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