CIIAITKK XXXV 

 STRUCTURE OF LEAVES 



433. Besides the framework or system of veins found 

 in blades of all leaves, there is a sofl tissue (408) called 

 mesophyll or leaf-parenchyma, and an epidermis which 

 covers the entire outside part. 



434. MESOPHYLL. Tin- mesophyll is not all alike or 

 homogeneous. The upper layer of it is composed of 

 elongated cells placed perpendicular to the surface of the 

 leaf. These are called palisade cells. The chlorophyll 

 (/ruins tin most abundant in them, because thej are <n the 

 side of the leaf mosl directly exposed to the sunlight. 

 Below the palisade cells is the spongy parenchyma com- 

 posed of cells more or less spherical in shape, irregularly 

 arranged, and provided with many intercellular air cavi- 

 ties. Pig. Ill ; also Pig. 115. In leaves of some plants 

 exposed to strong lighl there may be more than one layer 

 of palisade cells, as in m 



the In-lia-ruhher plant , / 

 an.l oleander. I vv when 



grown in bright lighl tB ^ 

 will develop two Buch 

 layers of cells, but in 



shaded places i! ma.N he m , 



found as in Fits 111. ' '""' ^m n 



Sudi plant - a> iris and 



compass plant . which pi,, 



nave l.oth Biirtaees "t 



the leaf equally exposed to sunlight, usually have a palisade 



la j er beneal h each epidermis. 



