274 



TYPICAL FLOWERING PLANTS 



cells of 

 epidermis 



'---stoma 



gu-^rd cell 



Figure 267. — Epidermis 

 of Leaf. 



leaves which grow with the blades in a horizontal position, 

 because there the stomata are protected from water which 

 would interfere with their action. Leaves which are 

 nearly upright have the stomata on both sides, and leaves 

 like a water lily that rest on the surface of the water have 

 the stomata on the upper surface. Stomata are both small 



and numerous. A dozen or more 

 are found in some leaves in a circle 

 no larger than a period on this 

 page. 



During a season a large amount 

 of water passes off through the 

 stomata of any plant. The pro- 

 cess of giving off this water is 

 called transpiration. This pro- 

 cess is unavoidable. The root hairs gather water almost con- 

 tinuously, and this is carried to the leaf by the fibrovascular 

 bundles and distributed to the cells. The mesophyll in 

 the leaf uses the minerals which the water contains, but 

 it does not use all of the water. This excess is cast off 

 into the spaces between the cells (intercellular spaces), 

 which communicate with the outside through the stomata. 

 Usually the transpiration takes place readily, but if the 

 outside air is not in condition to take up moisture, the 

 cells become too full and the excess is passed off through 

 organs (the hydathodes) at the ends of the vascular 

 bundles. The drops of water which escape from the ends 

 of the hydathodes are called guttation drops. Grass blades 

 and strawberry and nasturtium leaves show such drops 

 almost every morning in the spring. House plants like 

 fuchsia or impatiens will produce guttation drops if 

 covered for a few hours with a bell jar. Cool a portion 

 of the jar later, noting what happens. Give an expla- 

 nation of what you see. 



