CHAPTER XVI 



Palisade layer 



THE LEAF AS STARCH FACTORY 



100. Leaf characters. The most common fact about a leaf 

 is that it is flat and comparatively thin. Many kinds of leaves 



have stalks, or pedicels, and 

 all leaves have veins run- 

 ning through the flat por- 

 tion, or blade. There is no 

 shape that is common to all 

 leaves. They differ as to 

 the character of the edge. 

 Some are smooth, whereas 

 others have wrinkled, un- 

 even surfaces. Some kinds 

 are hairy, while others are 

 quite bald. Even the color 

 of leaves is not uniform, 

 though there is more or 

 less of the green chlorophyl 

 present in the leaves of all 

 plants. 



FIG. 23. Structure of leaf 



101. Unusual forms of 

 leaves. Most familiar leaves 

 are flat, spread-out structures. 

 Some plants, however, have 

 leaves that depart considerably 



from this model. There are leaves that are nothing more than fine hairs, 

 as on certain cactuses, others have extensions that behave like' tendrils, 

 and some are spines. Certain plants have leaves that are more or less 

 active in getting animal food. 



70 



tate 



This diagram shows the tip of a leaf with a 

 piece removed by two cuts at right angles to 

 each other, as it might appear under the mi- 

 croscope. Note the different kinds of cells 

 and tissues 



