CHAPTER V. 
THE LEAF. 
33. The Leaf.—A leaf is a lateral outgrowth of the stem 
and consists of three parts :— 
(a) The leaf-blade or lamina ; 
(b) The leaf-stalk or petiole ; 
(c) The leaf-base. 
The leaf-blade is the chief part of the leaf, and plays an 
important part in the feeding, respiration and transpira- 
tion of the plant. It is usually green, and may assume 
a variety of forms and shapes. In some cases the leaf- 
blade is not developed or dies away, and the petiole be- 
comes the most important part. The leaf-stalk or petiole 
is not always present. When absent the leaf is said 
to be sessile, when present, stalked. The petiole is usu- 
ally a cylindrical structure, but its internal structure 
resembles that of a leaf. In some cases it becomes 
expanded into a blade and usurps the function of the 
true lamina. It is then called a Puynuope (fig. 39). 
In other cases it may act as a climbing organ. Its chief 
function is to support the leaf in as advantageous a 
position as possible for carbon assimilation. 
The leaf base is often hardly distinguishable from the 
leaf stalk, but in many monocotyledons it is a highly 
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