THE STEM AND THE LEAF 69 
which active cambium remains, are said to be open. The 
palms and similar monocotyledonous trees cannot form an- 
Fic. 48. A young leaf 
of wild black cherry 
b7, blade, or expanded 
part; sta, leafstalk ; sti, 
stipules, or appendages at 
the base of the leafstalk 
nal forms of ordinary leayes and the 
parts of which they consist. 
At the base of the petiole many 
leaves bear a pair of appendages 
called stipules (figs. £8 and 49). In 
some leaves, as those of the pansy, 
nual rings of wood. There are, however, 
a few tree-like monocotyledons in which 
the trunk continues for years to increase 
in thickness, and may reach great dimen- 
sions, but these trunks do not thicken 
in the same way as do the trunks of our 
familiar trees. 
Many of the woody monocotyledons are 
remarkable for the extraordinary length 
and slenderness of their stems. The rat- 
tans, for example, often climb for hun- 
dreds of feet among the tops of tropical 
forest trees. 
68. The parts of the leaf. It already 
has been stated in section 11 that a leaf 
consists of pet- 
iole and blade. 
A few words 
may now be said 
about the exter- 
these form an important part of the Fie. 49. Tip of a geranium 
total leaf surface. Not infrequently. 
as in the black locust, the stipules 
(Pelargonium) shoot 
bl, blade of a leaf; bl’, blade 
of a young leaf, only partly ex- 
have the form of thorns, one at each panded from the naked bud; 
side of the base of the petiole. 
7, leafstalk; st stipules. Con- 
siderably reduced 
In general the form of the leaf 
depends very much on the distribution of the groups of fibro- 
vascular bundles known as veins. Most monocotyledons have 
