PECULIAR USES OF LEAVES 
289 
253. The Arrangement of Leaves. — Whatever the ar¬ 
rangement of leaves on any particular plant, the object is to 
expose the leaves most advantageously to light and air, inci¬ 
dentally preventing their shading one another, which some¬ 
times causes a vertical branch and a horizontal branch of the 
same plant to show a different arrangement of leaves. In 
general, leaf arrangement falls into two groups: (1) small 
leaves arranged all along the length of a branch — the spiral 
arrangement, the simplest form of which is found in the elm 
where the leaves are in two rows alternating with each other; 
(2) a few large leaves at the end 
of a branch, as in the maple, where 
the leaves are in pairs, each pair 
alternating with its neighbors. In 
the first case the shape of the leaves 
is such that all the space is occu¬ 
pied without much overlapping; 
in the second, every leaf is fully 
exposed to the light by the lowest 
leaves having the longest petioles. 
(See Figure 269.) The leaves of 
a maple illustrate this. A rosette 
is formed by leaves, arranged spi¬ 
rally on a very short stem, with long petioles nearest to the 
ground, shorter ones alternating with them and filling the 
spaces. The dandelion, evening primrose, and thistle show 
rosettes. Light that has passed through one leaf is of little 
value to a leaf below it. Some plants have finely divided 
leaves, an adaptation which prevents any leaf shutting off 
all the light from those below. Angular leaves, round leaves, 
and leaflets are all adaptations to use up all the space with¬ 
out overlapping. 
254. Peculiar Uses of Leaves. — Some leaves, like the sun¬ 
dew, pitcher plant, and Venus’s flytrap, are adapted for catch¬ 
ing insects for the use of the plant as food (see page 366). In 
