FORM AND STR " 



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

 dividual leaf : 



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

 Condnplicate, 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, 



i;o6 



