CHAP. II. 
LEAVES. 
143 
parenchyma of the leaves: in the former 
case they project beyond the surface or 
margin of the leaf, as in many Solana and 
the Holly (Ilex aquifolium) : in the latter 
they are the veins themselves become hard- 
ened, as in the palmated spines of the 
Barberry ; the spiny petiole of many Le- 
guminous plants is of the same nature 
as the latter. So strong is the tendency 
in some plants to assume a spiny state, 
that in a species of Prosopis from Chili, 
of which I have a living specimen now 
before me, half the leaflets of its bipinnate 
leaves have the upper half converted into 
spines. 
2. Of Stipules. 
At the base of the petiole, on each side, is frequently seated 
a small appendage, most commonly of a texture less firm than 
the petiole, and having a tapering termination. These two 
appendages are called stipules. They either adhere to the 
base of the petiole or are separate ; — they either endure as 
long as the leaf, or fall off before it ; — they are membranous, 
leathery, or spiny ; — finally, they are entire or laciniated. 
