36 LOCATION OF STOMATA 



easily demonstrated by dipping a leaf of a water lily or spatter 

 dock in the water. When the leaf is removed the water runs 

 off of the waxed surface without wetting it. Some leaves are 

 more or less erect, as the cattails, rushes and grasses, and these 

 have the stomata developed more or less evenly on both surfaces. 

 Doubtless the intense light of midday is not beneficial to these 

 leaves and the blade of the leaf is consequently placed parallel 

 with the sun's rays. This arrangement of the leaf permits a 

 direct illumination of the leaf only in the morning and afternoon 

 when the intensity of the light is feebler. Leaves develop fewer 

 stomata in a dry atmosphere and intense light than in moist and 

 shady places. Light and moisture also influence the position of 

 the stomata in another interesting way. Plants living in the 



Fig. 24. Cross-section of a leaf of the inch plant, Tradescanlia, showing 

 the delicate character of the cells and the raised stoma of this shade-loving 

 plant. 



shade or in the presence of an abundant soil-moisture develop 

 the stomata on a level with the leaf surface (Fig. 24), because 

 there is no necessity of conserving the water supply. For the 

 same reason some aquatics have lost altogether the power of 

 closing their stomata. On the other hand plants that are exposed 

 to arid conditions or drying winds develop the stomata well 

 below the surface of the leaf, as in the cactus and in the needles 

 of conifers (Fig. 23, s), or in furrows, as in certain grasses, 

 or at the bottom of minute pores, as in the oleander. These 

 depressions remove the stomata from the dry winds and prevent 

 the direct contact of the moist air in the leaf with the dry atmos- 



