Welcome to You Ask Andy

Danny Ford, age 14, of Lansing, Michigan, for his question:

Does a tree grow from the top or the bottom?

The most eye catching garden trees are trained to grow in artistic shapes. A patient gardener spends years coaxing their trunks and branches to hug a wall or to stand out in a trim geometrical shape. He must know just how a tree grows, also where and when to expect it to sprout new growth.

As a person grows taller, his body seems to sprout upwards from ground level. If this were actually so, it would be logical to expert trees to sprout upward from the ground. And in a way, so they do. A growing tree rises higher and higher. Your hair certainly grows longer from the roots. A tree seems to push up taller from its roots in much the same way. However, the actual growth of a tree does not occur in this manner.

Youv.:Christmas tree is (or was) ai evergreen conifer with a wide fan of branches at ground level, tapering to a point at the top. If it has roots and you plant it in the garden, do not expect the trunk to push up from the soil, adding new lower branches as it grows. If your lucky tree establishes itself, its future growth may surprise you. The trunk will grow taller by adding new growth at the top. The branches will grow wider by adding new growth at their tips.

The base of the tree at ground level stays just where it is. However, it will get a bit wider and stouter with every growing season. As your young conifer becomes a teenager, you may be disappointed to see that some of its lower branches wither and fall. The lower trunk grows barer and fatter, but no new growth pushes up from the earth. Many pines drop their lower branches as feathery fronds of new foliage a=e added at the top. When the tree gets through its shaggy teenage stage, its crowning greenery is supported high on a straight, sturdy trunk.

The growth cells of a plant are just below the skin or bark. During the growing season, these cells divide and each becomes a pair of daughter cells. Usually the cell on the outer side continues the role of a growth cell and multiplies. Sometimes it may add its woody walls to the bark. The inside cell, as a rule, takes up the chores of the ordinary woody cells that tote nourishing sap up and down the tree.

In any case, the growth cells form a thin layer under the skin of the tree. They surround the rim of the trunk, the sides and tips of the boughs and branches. These and only these cells can grow new cells. Hence a tree grows thicker around its trunk and branches, the tips of its twigs grow longer and spread wider. The top of its crown grows taller. But no new growth pushes up from the ground. Meantime, its roots also grow thicker and their growing tips probe deeper into the soil.

The cells rF a conifer are seeped with tacky resins. When branches fall from its growing trunk, the wounds are healed and sealed with this gummy material. Later the trunk adds new circles of cells around itself and the teenage wounds become buried in layers of new wood. If the tree is felled, a slice of its wood will show these hard, dark scars as knots in the woody lumber. The slice also shows the grained ridges of woody layers added during past growing seasons.


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