Welcome to You Ask Andy

Jerry Weikle, age 10, of Newport News, Virginia for his question:

How do seedless oranges reproduce?

Oak trees grow from acorns and beans produce bean plants. In nature, seeds are expected to produce plants like their parents. This is how nature worked for billions of years to clothe our world with greenery, flowers and fruits. Then came mankind, the patient gardener. He worked in partnership with nature. Together they produced and reproduced an endless variety of improved plants.

Seedless oranges are possible because gardeners found ways to improve nature's wild oranges. The original varieties bore sour little fruit called bitter oranges. However, those sturdy wild trees could survive a lot of hardship in the wilds. Gardeners selected the best types, pampered them and cross pollinated them to produce better fruit. But their pam¬pered trees were less sturdy and sometimes the seeds were useless.

However, they discovered a faster, surer way to reproduce their biggest sweetest oranges. The miraculous method is called grafting  ¬and grafting does not depend upon seeds to produce seedless oranges. It depends upon an amazing layer of plant cells called the cambium.

No doubt you have wondered how a tree adds new rings of wood around its trunk. They are created by the cambium, a thin layer of growth cells that lies just below the bark. And it so happens that the cambium layer around one tree can unite with the cambium around a twig or trunk of another tree. This is the secret of grafting.

A grafted tree is actually two in one. It grows together from a rootstock and a scion. As a rule, the rootstock of a seedless orange tree came from a bitter orange tree, similar to its sturdy wild ancestors. The scion is a twig, taken from the boughs of a pampered seedless orange tree.

To make the graft, the stem of a young rootstock tree is cut down. The bark is tenderly sliced and peeled back to expose the layer of cambium. The scion twig is sliced so that cambium cells are exposed at the cut surface. Then the twig is placed so that its cambium is in close contact with the cambium of the rootstock. The grafted surgery is sealed in place and the two layers of cambium grow together as one.

In time, the grafted twig becomes the trunk and boughs of an orange tree. Because it grows from a twig taken from a seedless orange tree, it too will produce seedless oranges. Meantime the rootstock grows the strong sturdy root system that feeds and supports the seedless tree. Maybe the rootstock grew from the seed of a bitter orange. But no seed was needed to grow the top of the grafted tree, which produces the seedless oranges

As a rule, the seeds of our pampered orchard trees produce stringy little fruits, like their wild ancestors. For this reason, most of them are grafted trees. Their rootstocks come from sturdy trees that bear poor fruit. Their trunks and boughs grow from grafted scions taken from trees that bear big, juicy fruit. And all this is possible because patient gardeners work in partnership to improve Nature's plants.

 

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