THE ORGANIZATION OF THE PLANT 



71 



from the soil. The points upon the stem where leaves originate 

 are called nodes, and the spaces between are internodes. Leaves 

 occur singly or in pairs at the nodes. When complete a leaf 

 consists of a flattened green portion, the blade ; a stemlike part, 

 the petiole ; and where the petiole joins the stem, two earlike 



FIG. 55. Leaf show- 

 ing pinnate venation 



The geranium leaf on 

 page 53 illustrates pal- 

 mate venation 



A "'' B 



FIG. 56. Two forms of parallel venation 



A , lily of the valley, veined from base to apex ; 

 B, canna, veined from midrib to margin 



or strap-shaped green parts called stipules. The stipules are 

 frequently absent, or they may take the form of spines or ten- 

 drils. Ramifying through the blade are strands of heavy tissue 

 called veins. These are really fibrovascular bundles which 

 serve to distribute food materials to the cells and aid in keep- 

 ing the blade expanded. Monocotyledons and dicotyledons 



