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Branch or Branches - First, much work has been done by Dr. Shigo on branches and how they are attached to trees.   A great piece of work is the World Wide Pruning Guide of his. He has dissected tens of thousands of trees in an attempt to have a better understanding of “branches” and the correct method of removal of the latter.
    Did you know that one of the most important events in the evolution or development of trees was the development of multiple growing points – branches? Not to be confused with sprouts. Palms, tree ferns and the ancient trees had one meristem or growing point. Trees in warm climates could survive with one meristem because there was no dormant period and the major survival factor was space to grow. So the upward rapid growth had survival value. They really had no room for lateral growth. So as multiple meristems began to appear on trees , this gave them opportunities to “move” or “grow” into new places. Now space was no longer the major limiting factor, temperature was. The multiple meristems gave the tree more opportunities to survive as harsh temperatures killed many, but not all of the meristems. The development of a branch was still not that simple. In a sense, the branch had to have a strong enough attachment so it would stay on the stem during winds, snow and ice, a new condition. Also at the same time, the branch had to have a way of separating itself from the stem when the branch died. So on one hand the branch had to be strongly attached and on the other hand it had to be very weakly attached. I believe how this dilemma was “solved” is one of the wonders of nature. The branch tissues mature before the parent stem tissues. The branch tissues do not grow into the parent stem, but instead they turn abruptly at the base of the branch and form a ring or collar of tissues that meets below the branch. This small strip of tissues below the branch lies on the trunk, but can hardly be called a structural attachment. After the branch tissues slow their growth, the trunk tissues begin to grow and to form a ring or collar of trunk tissue over the branch collar. Every growth period the trunk collars envelop the branch collars. In a sense, in a sense, the branch is not really tied into the trunk but is held by a series of trunk collars. As a branch begins to die, within the base of the branch, a protection zone that contains antimicrobial substances begin to form. Branch-inhibiting organisms grow into the protection zone and usually stop. Decayed wood at the base of branches facilitates shedding. I believe this is a succession of microorganisms. In conifers, protection resins may form outward into the branch. The branch receives water and elements in the pathway of tissues that form the branch collar. Water and elements are transported towards the leaves or needles in the xylem and food made by the leaves or needles is transported toward the sink in the phloem or the inner bark. Water, elements and food do not move from branch to branch, nor do other substances. These points are made for branches that have wood of more than one-growth-increment old. I think transport may go both directions in primary tissues or in tissues that are one-growth-period old.
    Let me share a true story with you that happened to me. In 1991 I was working on a tree in Florida and I did not know the difference between a branch and a sprout. I was climbing and I roped into a sprout not knowing it did not have a branch collar thus weakly attached. To make a long story short, I quickly learned as I fell through the pool area roof, almost into the pool, that there is a serious difference between a sprout and a branch. Source A NEW TREE BIOLOGY DICTIONARY by Dr. Shigo.

For much more on branches see;

A NEW TREE BIOLOGY

MODERN ARBORICULTURE

A WORLD WIDE PRUNING GUIDE

by Dr. Shigo for starters.