33 
ders it impossible to mistake a Plane leaf for a 
Vine leaf. In what does that difference consist ? 
In the Vine each rib has 
a number of strong curved 
lateral-arms which set off 
at a particular angle, 
branching in a peculiar 
manner, and if not seen 
nevertheless indicated, by 
the little variations of light 
and shade which their in¬ 
numerable ramifications, 
and the consequent eleva¬ 
tions of surface, produce. 
Whereas, in the Plane leaf, although we do not find 
the arms missing, yet they are very much less curved, 
and the side veins are so sunk in the leaf as to pro¬ 
duce little inequality of surface, but to leave the leaf 
almost flat. Nor is this all. In the Plane the ribs 
do not quit the stalk as they do in the Vine leaf, and 
hence again arises a characteristic difference. In the 
Vine, the principal ribs radiate from a common point, 
situated exactly where the stalk joins the leaf. In 
the Plane, the principal ribs spring from a point at a 
considerable distance above the place where the stalk 
joins the leaf. Out of this, not to mention other im¬ 
portant peculiarities in the veins, grow some of the 
characteristic features which enable the eye uncon¬ 
sciously to distinguish a Vine leaf from a Plane leaf; 
and so in other cases. 
74. As a general rule, it will be found that the ar¬ 
rangement of veins on one side of a leaf is the same 
on the opposite side, so that, as was before observed, 
each side of the leaf balances the other. In reality, 
B 5 
