6 OF THE LEAF AND ITS PARTS. 
which is called the blade (pl. 2. f.1. 1.), and is thie 
principal part of the leaf; to this blade there is a stalk 
(p-), on which the blade is supported and joined to the 
stem, this is called the leaf-stalk: the rounded part of 
the blade, where it joins the leaf-stalk, is called the base, 
and the narrow end, or point, the apes of the leaf; the 
edges are termed the margins. On examining the blade 
on its under surface, or that which is turned towards 
the ground while the leaf is on the plant, it will be 
found to be of a lighter colour than the upper, and the 
leaf-stalk will be seen passing in the form of a vein 
from the base to the apex of the leaf; this is called the 
mid-vein, or mid-rib of the leaf, and from it may be 
‘seen passing a number of other ribs, or veins as they 
are usually called, towards the edges or margins of the 
blade. 
8. The principal parts then of a leaf are as follows 
(pl. 2.), the leaf-stalk, called also the petiole, the blade 
or limb of the leaf, the base, which is always directed 
towards the stem, the apex, the edges or margins, the 
upper and the under surface, the upper being gene- 
rally darker than the under, which has the mid-rib and 
veins much more strongly marked upon it than the 
upper. Through the leaf-stalk a number of fine fibres 
pass into the blade and divide there in the form of 
veins, which will be more readily seen by holding the 
leaf up to the light; these veins form the frame-work 
or skeleton of the leaf (pl. 2. f. 1.), while all the spaces 
between the net-work of veins are filled up with a 
delicate thin green substance. Skeleton leaves are 
found at the latter end of autumn, in consequence 
