English for

6.4 Reading #1
: Structure of a Typical Leaf
 
Each leaf typically has a leaf blade called the 
lamina
, which is also the widest part of the 
leaf. Some leaves are attached to the plant stem by a 
petiole
. Leaves that do not have a petiole and 
are directly attached to the plant stem are called 
sessile
leaves. Small green appendages usually 
found at the base of the petiole are known as 
stipules
. The majority of leaves have a midrib that 
runs the length of the leaf and branches out to the sides to create vascular tissue veins. The margin 
refers to the leaf's edge. A typical eudicot leaf's structure is depicted in Figure 107.
 

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163 
 
Figure 107.
A leaf is a deceptively simple-looking structure that is extremely effective.
 
 
Veins are created by the vascular tissue within each leaf. The 
venation
pattern refers to how 
the veins are arranged in a leaf. Differences between the venational patterns of monocots and dicots 
(Figure 108). Monocots have parallel venation, which means that the veins run parallel to one another 
rather than converging at a point along the length of the leaf. However, in dicots, the leaf's veins 
resemble a net and form a pattern called reticulate venation. The Ginkgo biloba is one existing plant 
that has dichotomous venation where the veins fork. 
 

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164 
Figure 108. 
(a) Tulip (
Tulipa
), a monocot, has leaves with parallel venation. The netlike venation in 
this (b) linden (
Tilia cordata
) leaf distinguishes it as a dicot. The (c) 
Ginkgo biloba
tree has 
dichotomous venation
79
.