TRANSPIRATION 1 7 



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 ^i^^^ / V 



accompanying Fig- >j5^X~(^-''''^ 1 '^ (f 



ures, as stomata. \W~^^r^^^~XY^ ~)ni^/S^rSp 

 Examine a portion y^<i©VC«o^ ~ — ^^^^^-^ 

 of the epidermis Xhx^^t-^A 

 from the upper side *-^I]?''^%^ ^ 



of the leaf ; are the 7.— stomata of an oak leaf: A, a small piece 



stomata distributed (highly magnified) with under epidermis removed 



n Vv fK 'A *° show stomata, ^, and minute hairs, h. B, a 



equally on DOtn SiaeS, stoma in vertical median section, cut across its 



and if not on which longer axis; a, intercellular space; ^, guard cell; 



, 1 . 1 -, ^1 orifice of stoma. 



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 1 



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 EOT. — 2 



