IV. STRUCTURE OF THE FOLIAGE-LEAF (e.g., Lilac 



leaf) 



A . External Characters: 



1. Make a drawing, natural size, showing all the parts 

 of the foliage-leaf given you, as seen from the under 

 side. 



2. Identify the following parts, and label them suit- 

 ably on your drawing: 



(a) The flat, expanded blade. Describe its colora- 

 tion (i.e., the kind and distribution of color). 

 Is the blade simple (i.e., not divided into leaf- 

 lets), or compound (i.e., branched, divided into 

 leaflets) ? The surface that lies uppermost, as 

 the leaf bends back from its position in the bud, 

 is the ventral surface; the under surface is the 

 dorsal one. These terms are applied with ref- 

 erence to the position of the leaf in the bud. 



(b) The leaf-apex, which is also the apex of the 

 blade. 



(c) The margin of the blade. 



(d) The base of the blade. 



(e) The venation (distribution of veins in the blade) . 

 Describe it as parallel-veined, pinnately netted- 

 veined (with a midrib), or palmately netted- 

 veined. Describe the difference between the 

 three types of venation. Is there a marginal 

 vein? If so, suggest what advantage it may 

 be to the leaf. 



(/) The petiole (stem of the leaf). Leaves having 

 a petiole are petiolate, otherwise sessile. 



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