120 
ORGANOGRAPHY.. 
BOOK I. 
of the parenchyma of the leaves: in the 
former case they project beyond the sur- 
face or margin of the leaf, as in the Holly 
(Ilex aquifoliiim) in the latter case they 
are the veins themselves become har- 
dened, as in the palmated spines of the 
Barberry. The spiny petiole of many 
Leguminous 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. 
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. 
By Link they have been called Paraphyllia ; an unnecessary 
