180 GENERAL DESCRIPTION OF THE PETIOLE. 
leaves, and in those of a compound character in which the leaflets, 
are sessile ; or it is compound, as in the Rose, when it divides 
into two or more portions, each of which bears a leaflet (fig. 378), 
or it is still more compound when the blade is further divided. 
The branches of the petiole or the stalks of the leaflets are then 
called petiolules, stalklets, or partial petioles; while the main 
petiole is termed the rachis or common petiole. 
The petiole is frequently more or less contracted at the base 
where it joins the stem owing to the presence of an articulation 
or joint (fig. 372, f). Leaves thus furnished with an articulated 
petiole fall away from the stem after they have performed their 
functions ; and in doing so they leave a scar or cicatria (fig. 207, 
b, b). This cicatrix commonly exhibits on its surface several 
little points, which are produced by the rupture of the fibro- 
vascular tissue of the petiole. The outline of the cicatrix and the 
arrangement of its ruptured fibro-vascular tissue vary much in 
different species of plants, and thus frequently form characters 
by which we may distinguish one plant from another after the 
leaves have fallen ; thus the varying appearance of these scars 
may be well seen by comparing a branch of the Ash with that of 
the Horsechestnut. 
In compound leaves the petiole is not only generally arti- 
culated to the stem, but the partial petioles are also frequently 
jointed to the common petiole, so that each leaflet becomes 
detached separately when the leaf begins to decay, as in the 
Sensitive Plant. By many botanists, indeed, no leaf is con- 
sidered truly compound unless it presents this characteristic ; 
consequently all leaves however much divided, and apparently 
compound, but which have not their separate portions articu- 
lated, are considered simple. Such a distinctive character cannot, 
however, be well carried out in practice, and when we consider 
that the presence of an articulation is by no means constant 
even in simple leaves, we can see no sufficient grounds for in- 
sisting upon this character in the separate portions of a leaf as 
evidence of its compound nature. The distinctive characters of 
simple and compound leaves as adopted in this Manual have been 
already fully treated of under the head of Composition of Leaves. 
(See page 162.) 
The presence of an articulation is to some extent a character 
of distinction between the three great divisions of plants. Thus 
the leaves of Dicotyledons are in the majority of instances 
articulated ; while those of Monocotyledons and of Cormophytes 
are non-articulated. Hence the leaves of the two latter, when 
they have performed their functions, instead of falling away and 
leaving a cicatrix as the former, decay gradually upon their re- 
spective plants, to the stems and branches of which they thus give 
a ragged appearance. There are many instances, however, in 
which the leaves of Dicotyledons are not articulated, asin the Oak. 
In such cases, the leaves, although dead, remain attached to their 
