The fifty kinds of oak trees that are native to America are about evenly
divided on the two sides of the Rocky Mountains. No Western oaks are
found in the Eastern states, and none of our Eastern kinds grows wild on
the other side of the mountains. The backbone of the continent is a bar
that neither group has been able to pass.
To know fifty different kinds of oaks by sight, so as to call each one by
its right name, is not an easy task; and yet it is not so difficult as it
at first might seem. To begin with, any tree we meet, which bears acorns,
we at once recognise as an oak. By this one sign, we are able to set this
great family apart from every other tree. As soon as they are old enough,
all oaks bear acorns. If a tree which we suspect to be an oak has no
acorn to show us, on or under the tree, a little close looking will
usually find some acorn cups still hanging on, or lying where they fell
upon the ground.
The leaves of oaks are distinctive. In general, they are all simple, and
their outline is oval. The borders are variously cut by deep or shallow
bays, between sharp points or rounding finger-like lobes. They are
leathery in texture, compared with leaves of most trees. After a little
practice, we learn to recognise oak leaves, no matter how variously cut
their borders may be.
In spring the flowers of oaks come out with the leaves. A fringe of
catkins at the base of the new shoot is composed of pollen-bearing
flowers. In the angles of the new leaves farther up the stem, we shall
find the little acorn flowers, usually in twos. This is the flower
arrangement of all the oaks; staminate and pistillate flowers on the new
shoots, separate and very different from each other, but always close
together, and always both kinds on each tree. The fringe of catkins falls
as soon as the pollen is shed. Little, red, forked tongues are thrust out
by the pistillate flowers to catch the golden dust when it is flying
through the air, and thus to set seed. All through the summer, the little
acorns are growing. We can find them in their tiny cups in the angles of
the leaves.
In the autumn the acorns are ripe, and falling. Some trees will show
acorns of two sizes, half-grown ones on the new shoots, and full-sized
ones on the bare twigs, just back of the new shoots.
This peculiarity divides the oak family into two great groups. One group
is composed of trees which have light-coloured bark, bear a crop every
year, and in winter are bare of fruit. This is known as the White Oak
Group. Its leaves have rounded margin lobes which do not end in sharp
points, as many of the lobes of oak leaves do.
All of the oaks whose leaves have pointed, spiny lobes on their margin
belong to the Black Oak Group. The bark of these trees is usually
dark-coloured. The acorns require two years of growth. For this reason,
there are half-grown acorns on the tree all winter, waiting for the
second summer to bring them to maturity. Every autumn the acorns which
are ripe are found on the twigs just back of the leafy shoots, which grew
during the past summer. These acorns have completed their second year of
growth.
When we hear any one speak of annual-fruited and biennial-fruited oaks,
we know that the White Oak and Black Oak Groups are meant. If you see an
oak tree whose leaves are cut into sharp pointed lobes, you will find
acorns of two sizes on its twigs. If you look across the fence and see a
pale-barked oak with finger-lobed leaves, and not a spiny point on their
margins, you will know that acorns of but one size will be found. Fix
these three points in mind. Then study all the oak trees you can find.
Trees of the White Oak Group have:
1. Rounded lobes on their leaf margins.
2. Acorns ripe in a single season.
3. Pale-coloured bark.
Trees of the Black Oak Group have:
1. Spiny-pointed lobes on their leaves.
2. Acorns requiring two seasons to ripen.
3. Dark-coloured bark