STRUCTURE AND PHYSIOLOGY OF PLANTS 11 



many soft plant cells. These cells have very thin walls 

 and are bathed by air. The air cavities are shown at A in 

 the figure. All the cells shown with dark grains in the figure 

 contain the green coloring matter of the leaf. This is called 

 chlorophyl (klo-ro-fil). The use of this will be spoken of later. 



Fia. So. Growing plants absorb moisture from the soil. Two flower-pots 

 with equal amounts of the same kind of soil are set in lard pails having water up to 

 the line shown. Corn is growing only in the left one. (Agricultural Education.) 



FIG. 36. Evaporation of water from leaves. The condensed moisture shows 

 in the upper part of the glass inverted over the growing plant. (Agricultural 

 Education.) 



EXERCISE. Skin of Leaf. Break a leaf partly in two 

 in such a manner as to peel the surface away from the inner 

 cells. This surface layer of cells is clear and contains no 

 chlorophyl, as shown in Fig. 4. The outer layer of cells is 

 so thin and clear that sunlight may pass through and reach 

 the green cells of the inner part of the leaf. 



Air Openings. Air may enter the leaf through small 

 openings, chiefly on the under side. One of these openings 

 is marked S in Fig. 4. These are called stomates, the word 

 meaning "mouths. " There are great numbers of the sto- 

 mates on the under surface of leaves. They may be opened 

 or closed according to the condition of the weather. This 

 is done by the action of a pair of cells at the opening called 



