CHAP. II. 



LEAF. 



89 



« 



1. or the Leaf. 



48 49 



The leaf is an expansion of the bark at the base of a leaf- 

 bud, prioi' to which it is developed. In most plants it con- 

 sists of cellular tissue filling up the interstices of a net-work 

 of fibres that proceed from the stem, and ultimately separating 

 from the bark by an articulation ; in many Monocotyledonous 

 plants. Ferns, and Mosses, no articulation exists, and the base 

 of the leaf only separates from its parent stem by rotting 

 away. 



This difference of organisation has given rise to a distinc- 

 tion, on the part of Oken, between the articulated leaves of 

 Dicotyledons and the inarticulated leaves of Monocotyledons 

 and Acotyledons : the former he calls true leaves, and dis- 

 tinguishes by the name of Lauh ; the latter he considers 

 foliaceous dilatations of the stem, analogous to leaves, and 

 calls Blatt. 



A leaf consists of two parts ; namely, its stalk, which is 

 called the stalk or petiole [Jig. 4.5. a), and its expanded surface, 

 which is called the blade or lamina (Jig. 45. c, h, d) : in ordi- 

 nary language the latter term is not employed, but in very 

 precise descriptions it is indispensable. 



The point where the base of the upper side of a leaf joins 

 the stem is called the axil ; any thing which arises out of that 

 point is said to be axillary. If a branch or other process 

 proceeds from above the axil, it is called supra-axillary ; if 

 from below it, infra-axillary. 



