112 
ORGANOGRAPHY. 
BOOK I. 
1. Of the Leaf. 
47 48 49 50 
The leaf is an expansion of the bark at the base of a leaf- 
bud, prior to which it is developed. In most plants it con- 
sists of cellular tissue, filling up the interstices of a net-work 
of fibres which proceed from the stem, and ultimately sepa- 
rating from the bark by an articulation; in many Mono- 
cotyledonous 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, w-hich is 
called \he petiole (Jig» 48. a), and its expanded surface, which 
is called the blade or lamina (Jig. 48. c, d) : in ordinary 
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. 
