LEAVES OF DICOTYLEDONS AND MONOCOTYLEDONS. 189 
inwards of the two margins of a phyllode, which unite below, 
and form a hollow body or pitcher ; but they are still separate 
above, and thus indicate its origin. The origin of the pitcher 
from the phyllode is, however, probably best seen in a species 
of Heliamphora (fig. 392), in which the union of the margins 
of the phyllode is even less evident than in the Sarracenia. 
In the Nepenthes (fig. 390) again, the petiole first expands intoa 
phyllode, then assumes the appearance of a tendril, and ulti- 
mately forms a pitcher, p; this is closed above by a lid, J, 
called an operculum, which is united to it by an articulation. 
The lid is here commonly regarded as a remarkable transform- 
ation of the blade; but some consider that the pitcher is 
formed out of the lamina, and that the operculum is the 
terminal lobe. This kind of pitcher is also looked upon by 
others as a modification of such leaves as the Orange (jig. 
320), and Venus’s Fly-trap (fig. 375), in which the petiole, p, 
is articulated to the blade; thus, if we suppose the winged 
petiole of such plants to fold inwards and unite by its margins, 
a pitcher would be formed resembling that of Nepenthes, and 
the jointed blade would then be seen to be clearly analogous to 
the operculum or lid of that plant. In another of these plants, 
the Dischidia, the pitchers are considered to be formed by the 
folding inwards and union of the margins of the blades. 
8. LEAVES OF DICOTYLEDONS, MONOCOTYLEDONS, AND 
CORMOPHYTES. 
We have already seen, in describing the structure and general 
characters of stems and roots, that these organs present well- 
marked distinctive characters in the above divisions of plants. 
The leaves of plants in the corresponding divisions, as we have 
noticed generally in their description, also present certain marked 
differences, which may be summed up as follows :— 
1. Leaves or DicoryLtepons.—In these the venation is 
reticulated in consequence of the veins branching in various 
directions and the divisions becoming united with one another, 
so as to form a more or less angular network (jig. 314). But 
in some plants, as Ranunculus Lingua and R. Flammula, the 
so-called blades have parallel veins, and have been therefore 
considered by some botanists as representing exceptions to the 
ordinary reticulated venation of Dicotyledons ; but these, as we 
have just seen (page 188), are not usually regarded as true blades, 
but as phyllodes or transformed petioles, from which they only 
essentially differ in being placed horizontally. 
The leaves of Dicotyledons are also very commonly articu- 
lated to the stem or branch, often compound, and variously in- 
dented or incised at their margins. Stipules are also frequently 
present. 
2. Leaves oF MonocotryLepons.—In these the venation is 
