THE LEAF. 



21 



these lines, which are darkened in Fig. Y, are, in the 

 living leaf, filled with green matter. 



FIG. 6. 



You know the names of 

 the parts of a leaf, and the 

 two following pictures will 

 show you what to call the 

 different parts of the frame- 

 work. 



RIBS. The stoutest 

 pieces of the framework that 

 begin at the petiole and 

 reach quite across the blade, 

 are called ribs. When there 

 is but one, as in Fig. 8, it is 

 called a midrib. 



FIG. 7. 



FIG. 8. 



-Veinlets. 



Vein. 



-Midrib. 



of the pnpil into the complexities of the subject before the 

 simpler portions have been sufficiently mastered. 



Now, the aim of this book is carefully to guard against such 

 a result. These first observations are made without reference 

 to those combinations of characters by which plants are identi- 

 fied as belonging to a particular order, genus, or species. One 

 of our aims is to learn the elementary facts so thoroughly and 



