202 



STRUCTURE AND VITAL PROCESSES OF PLANTS 



plants. They are characteristic of certain families, e. g., the 

 Malvaceae, Leguminosse, Rubiacese, Euphorbiacese. Such stipules 





may also be modified and appear as thorns, as 

 for instance in the Acacia. 



2. The lilades of Leaves exhibit various 

 Characteristics: — 



(«) As to the arrange- 

 ment of their ribs or veins. 

 If we examine the leaves of 

 Grasses or Lilies, we shall 

 find that the veins 

 run parallel or al- 

 most parallel to the 

 mid-rib in one direc- 

 tion from the stalk 

 to the tip. The ve- 

 nation of such leaves 

 is said to be parallel. 

 The veins in most 

 dicotyledons, such 

 as the Teak and 

 Banyan, form a kind 

 of network; they are called net-veined (reticulated, hg. 184j. 



If the side nerves branch off from the mid-rib alternately or 

 opposite like the hairs of a feather, we call the leaves feather- 

 veiued or pinnately veined (Adhatoda). If they radiate from the 

 base of the leaf as the fingers from the palm of the hand, the 

 leaves are digitately or x)almately veined (Castor). 



{!)) As to their general form: Some are linear (liemidesmusj, 

 some obloitfi (Mango), some elliptic (Vinca), and some orbicular 

 (Jujube). If the broadest part of the blade is below its centre, 

 the leaf may ])e lanceolate (Gloriosa), or ovate (Ban^^an); if, 

 however, the blade is broader near its apex, it is oblanceolate 

 (Crotalaria retusa), or obovate (Cashew). 



(c) As to their base: acute (Mango), narrowed (Teak), cordate 

 (Betel), reniform (llydrocotylej, auricled ((^alotropis), sagittate 

 (Limnophytum), Jiasiate (Typhoniuin). 



Fig. 183. — Stipulate 

 leaf of Pea. 



Fig-. 184. — Piece of the 



leaf of a dicotyledonous 



tree with reticulated 



veins (reduced). 



