120 



LEAVES AND THEIR WORK 



number of vdns. These veins usually present a netted appear- 

 ance in the leaf of a dicotyledon, but nm more or less parallel 



to one another in the blade of 

 a monocotyledonous leaf. At 

 the base of the leaf may be 

 found a pair of outgrowths 

 from the petiole called stipules. 

 By means of these stipules in 

 the rose leaf, for example, we 

 are able to know that the leaf 

 is compound, that is, each of 

 the little leaflike parts is in 

 reality part of a leaf blade 

 that is so deeply indented that 

 the blade is cut away to the 

 leaf — ^for a pair of stipules is 

 complete leaf. These fall off 



Palmately-compound leaf of rose, show- 

 ing stipules (si). 



of the 

 every 



midrib, or central vein, 

 found at the base of 

 early in many leaves. 



The Cell Structure of a Leaf. 

 — The under surface of a leaf 

 seen under the microscope 



Surface view of epidermis of lower sur- 

 face of a leaf ; e, ordinary epidermal 

 cell ; g, guard cell. — Tschirch. 



Section of a leaf ; e, epidermis ; c, cells 

 containing chlorophyll bodies ; p, in- 

 tercellular passages ; g, g, guard 

 cells of stoma. 



usually shows nimibers of tiny oval openings. These are called 

 stomata (singular stoma). Two cells, usually kidney-shaped, are 

 found, one on each side of the stoma. These are the guard 



