I have an orange-tree question. Can anyone explain?

There are several different types of sharp structure on plants. They are derived from different parts of the anatomy and so are found in different places.

Spines are sharp structures derived from leaves or some kind of leaf scale. A typical type is on a cactus. They are always associated with the leaf axil of the plant and are typically found just below a leaf or branch.

Another type of sharp structure is simply a modified piece of bark, such as the prickles on roses. These are found scattered over the surface of the stems, not associated with leafs or sideshoots.

On Citrus trees, the sharp structures are modified branches, and so are typically found at the leaf axils just above leaves. They are short determinate branches where the tip has become sharp. These are typically known as thorns although the nomenclature is quite loose.

Hello !!!

in my many visits to Spain i asked that question of the orange grove farmers and the explanation they gave was.:>

It is there to stop people from pulling the fruit from the tree because such action can damage the tree.

One has to cut the fruit from above the thorn for protection. In other words stalk and fruit together.

Hmmm ... look at how things work. Traits are a composition of male and female attributes. Half the raw material comes from one and half from the other. Red parent could be pure red (RR), or half-red (Rw). To get 3 red vs 1 white when selving, parents must both be Rw. (Offspring are equally likely to be RR, Rw, wR, or ww). Albescens is the inherited "white" trait, so it's a recessive condition. Orange is reasonably natural ... in wild fruit at least ... so it's more likely to be the Red-white cross. To get albescens, the parents must both carry the recessive trait ... and it still isn't a guarantee that the offspring will show albescens. Most likely, the offspring will also be "carriers".