The first group is the largest, including as it does such large
families as the maples, oaks, willows, poplars.
The second group comes next with the well-known walnuts, hickories,
ashes, and buckeyes.
The third group is very small, there being but three well-known trees
bearing doubly compound leaves: the honey locust, Kentucky coffee tree,
and Hercules Club.
The three forms are shown at Fig. 242.
The leaf ends at the bud growing at the end of the leaf stem. All above
this bud constitutes the leaf, no matter what its shape or size, and
falls in the autumn, with a few exceptions.
The small leaflets on the compound leaf are simply parts of a leaf,
not separate leaves, as there are no buds at the point where they join
the stem. The arrangement of these leaflets varies. In the buckeye and
horse chestnut they radiate from a common point, while in the locust
they are in parallel rows on opposite sides of the stem.
[Illustration: Fig. 242. Three types of leaves]
In doubly compound leaves the leaflets are themselves compound, making
the whole leaf very large, those of the Kentucky coffee tree being
three feet in length.