FORM AND STRUCTURE 



The following are the common forms of folding of the in- 

 dividual leaf : 



Inflexed, bent inward toward the base. (Fig. 4.) 

 Conduplicate, two sides applied to each other, face to face. 



(Fig. 5.) 

 Plicate, when folded back and forth like the plaits of a fan. 



(Fig. 6.) 

 Convolute, when rolled inward from one margin to the other. 



(Fig. 7.) 



Involute, rolled inward from each margin toward the midrib. 

 (Fig. 8.) 



Revolute, rolled outward from each margin toward the mid- 

 rib. (Fig. 9.) 



Botanically the inner surface of a leaf is that which in 

 ordinary description is called the upper surface. 



VENATION. 



The Venation of a leaf is the arrangement of the veins or 

 framework. 



Three types are distinguished : 



Forked-venation, seen in ferns. 



Parallel-venation, seen in grasses and lilies. 



Netted-venation, the form that prevails among deciduous 

 trees. In the Netted-venation the veins branch re- 

 peatedly and the veinlets run together end to end, form- 

 ing a more or less complicated network. 

 There are three modifications of this type : 



Pinnate or Feather-veined, in which there is a midrib with 

 lateral branches called primary veins which run toward 

 the margin ; as in the leaves of the Elm, Beech, and 

 Chestnut. 



Palmate-veined, in which there are several ribs radiating 

 from the petiole to the margin ; as in the leaves of the 

 Maple and Sycamore. 



Ribbed-netted-veined, in which there are several ribs run- 

 ning from petiole to apex with a network of small veins 



between. 



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