41 



aims to give a general description of leaves and a brief outline of 

 their work. 



A typical foliage leaf consists of three parts: (1), the blade or 

 flattened portion (lamina) ; (2), the leaf-stalk (petiole) ; and (3), 

 the leaf -appendages (stipules). 



Two kinds of leaves are usually recognized: simple and com- 

 pound (Plate IV). Simple leaves have blades which are more or less 

 united into one piece, while in compound leaves each leaf is composed 

 of a number of smaller leaflets. Compound leaves may have all the 

 leaflets originate from one point as in the Buckeyes (Plates CXII, 

 CXIII), or scattered along the main petiole as in the Common Locust 

 (Plate XCVII). Each primary division of a compound leaf may 

 again be compounded as in the Kentucky Coffee-tree (Plate XCIV). 

 Such a leaf is known as a doubly compound leaf. 



The arrangement of the leaves on the twigs and branches of our 

 common trees may be alternate, opposite, or whorled (Plate IV). 

 When the arrangement is alternate, the individual leaves are located 

 singly at a node; when opposite, two leaves occur opposite each 

 other at a node; and when whorled, more than two leaves occur at 

 a node and are distributed regularly around the twig. In a few 

 species as the Birches, the leaves of the lateral spurs appear to be 

 opposite, but upon closer examination they are found to be alternate. 



The leaves of the trees native to this State may be classified as 

 follows: (1), Trees with needle-shaped leaves, known as conifers 

 or evergreens, and (2), trees with broad leaves known as hardwoods 

 or deciduous trees. The needle-shaped trees show a wide variation 

 in the form and distribution of their needles. They may occur 

 singly, in fascicles of 2, 3, or 5, or in clusters on lateral spurs; they 

 may also be stalked or sessile, scale-like or awl-shaped, and flat, 

 semi-circular, triangular, or four-sided in cross-section. The broad- 

 leaved trees have an even wider variation in form. This may be in 

 part due to the greater number of representatives belonging to this 

 order. A few of the commonest leaf forms are shown on Plate V. 

 Other intermediate forms are commonly found among our trees. The 

 size- of the leaves varies as much as their form. They may be small, 

 scale-like, or awl-shaped as in the Arbor Vitae and Common Juniper 

 respectively, or large and tropical-like as in the Magnolias and 

 Papaw. 



The point, or apex, of leaves varies with the species and the gen- 

 eral leaf -form. The commonest kinds of points recognized are 

 shown on Plate V. 



The bases of leaves are also often characteristic and of consider- 

 able value in distinguishing species, since different species may have 

 the same general form but different bases. The commonest kinds 

 of bases recognized are shown on Plate V. Intermediate forms may 



