CHAPTER III. THE LEAF. 



2 9 



In the reticulate plan the veins branch repeatedly, and the 

 veinlets, or small branches of different veins, run together end 

 to end, or anastomose, forming a more or less complicated net- 

 work. There are also three modifications of this type : (1) The 

 pinni-reticulate, or pinnately netted, in which there is a mid-rib 



Fig. 61. 



Fig. (a. 



Fig. oj. 



Fig. 60. — The leaf of the Calla ; a pinni-nerved leaf. 



Fig. 61. — The leaf of Carpinus ; a pinni-reticulate leaf. 



Fig. 62. — The leaf of the White Poplar ; a palmi-reticulate leaf. 



Fig. 63. — The leaf of the Wild Yam ; a costate-reticulate leaf. 



with lateral branches which run toward the margin, branching 

 repeatedly and forming a network, as in Fig. 61 ; (2) the palm i- 

 reticulate, or radiately netted, a reticulate leaf in which there are 

 several ribs radiating from the petiole to the margin, as in the leaf 

 of the White Poplar, Fig. 62, and (3) the costate-rcticulate or ribbed- 

 netted leaf, in which there are several prominent veins or ribs 

 running from base to apex of the leaf, with a network of small 

 veins between, as in the leaf of the Wild Yam, Fig. 63. The first 

 and third varieties incline to elongated and the second to 

 rounded forms, though there are some exceptions to the rule. 



The Forms of Leaves. 



Since leaves, like other organs of the plant, may remain 

 simple or branch, we may conveniently classify them into simple 

 and compound forms. The shapes of each are very numerous, 

 and as they often afford characters by means of which plants are 

 distinguished, it is important for the student to be familiar with 



