LEAVES 



29 



tions between different groups of plants. The blade is the most 

 obvious part and offers several important characters for com- 

 parison in classifying. In the mode of veining, in outline, mar- 

 gin, base, apex, and its surfaces, the blade must be studied by the 

 systematist. In the study of leaves those found on water-sprouts, 

 suckers, and those borne on slow-growing shoots or spurs are 



Fig. 17. Leaf of 

 common plum. 

 Pinnately veined ; 

 obovate ; apex 

 obtuse ; base ta- 

 pering ; margin 

 serrate. 



Fig. 18. Leaf of 

 peach. Pinnately 

 veined ; lanceo- 

 late ; apex and 

 base acute ; mar- 

 gins sinuate and 

 finely serrate. 



Fig. 19. Leaf of 

 sour cherry. Pin- 

 nately veined ; 

 obovate ; apex 

 acuminate ; base 

 abrupt ; margins 

 coarsely serrate. 



not taken, but, rather those produced by normal free-growing 

 shoots. 



46. Mode of veining. — The framework of a leaf consists of 

 tough fibrous veins and ribs which run from the stem through 

 the petiole into the blade and there spread out to the margin 

 of the leaf. The way in which these ribs and veins are dis- 

 tributed is called venation. The main branches in a system of 

 venation are called t^ihs of which there is usually a stout central 

 one known as the midrib. The ribs subdivide into smaller divi- 

 sions termed veins and these in their turn divide into veinlets. 

 There are two common types of venation : these are the parallel 



