TRANSPIRATION 



7. Stomata of an oak leaf: A, a small piece 

 (highly magnified) of under epidermis removed 

 to show stomata, g, and minute hairs, h. B, a 

 stoma in vertical median section, cut at right angles 

 to its longer axis ; a, intercellular space ; g, guard 

 cell ; s, orifice of stoma. 



examine it with a good lens. Hundreds of little eye-shaped 

 dots will be seen covering the surface, which can easily 

 be recognized, by 

 comparison with the 

 accompanying Fig- 

 ures, as stomata. i w^uj^V-W -IT 

 Examine a portion ^ 

 of the epidermis 

 from the upper side 

 of the leaf ; are the 

 stomata distributed 

 equally on both sides, 

 and if not, on which 

 are they thickest ? 

 Which side of the epidermis seems to be most active in the 

 work of transpiration ? 



17. Distribution of Stomata. While stomata are gen- 

 erally most abundant on the under side of leaves, where 

 they are protected from excessive light and heat, this 

 is not always the case. Similar openings occur also on 

 young stems, and are called lenticels. In vertical leaves, 

 like those of the iris, which have both sides equally ex- 

 posed to the sun, stomata are distributed equally on both 

 sides. In plants like the water lily, where the under sur- 

 face lies upon the water, making transpiration in that 

 direction impossible, they occur only on the upper side. 

 Succulent leaves, as a general thing, have very few, be- 

 cause they need to conserve all their moisture. Submerged 

 leaves have none at all ; can you tell why ? 



18. Protection of Stomata. In addition to their function 

 of transpiration, stomata permit the entrance to the interior 

 of the plant of atmospheric air containing carbon dioxide, 

 a gaseous substance used by them in the formation of food. 

 If they become choked up with water or other obstruction, 

 the leaves can neither exhale their superfluous moisture 

 nor take in air; hence these pores are protected by 

 hairs, wax, and other water-shedding appendages. Plunge 



ANDREWS'S BOT. 2 



