The unique structure of agarwood: "inter-wood phloem"

Everyone knows the four elements for identifying agarwood: "phloem, vessels, wood rays, wood fibers". Why can agarwood be identified only by these four elements?
The key here is: "inter-wood phloem"!
Key points: inter-wood phloem, inter-wood phloem

To be specific, this is the case:

We all learned basic botany knowledge in junior high school. The xylem and phloem of trees are separate, the xylem is inside and the phloem is outside. One is responsible for transporting water and the other is responsible for transporting nutrients (if I remember it wrong, please correct me in time);

After recalling the junior high school knowledge, let's go deeper. As mentioned earlier, the phloem of most plants is only a thin layer, which is located in the outer part. This is very strange. If the phloem is only a thin layer, why do we see phloem on agarwood, and the phloem and vessels (which should be xylem) are intertwined with each other?

, This involves a unique structure of the "Aquilaria genus of the Thymelaeaceae": "inter-wood phloem". As the name suggests, the name "inter-wood, inter-wood" means that "the phloem" grows in the "xylem". Unlike other trees, the "phloem" and "xylem" are completely layered. There are not many plants with "inter-wood phloem". Until now, botanists have not figured out whether this is progress or regression in the history of plant evolution, but "inter-wood phloem" is crucial to the production of agarwood, which is why only a few tree species can produce agarwood (see the picture for some information related to "inter-wood phloem");

, Plants with "inter-wood phloem" are usually tall plants. It is rare to hear that rattans need such a strong structure to cope with survival crises. Therefore, in the general sense, if a piece of thing has the "four elements of agarwood appearance" at the same time and can "smell", then it can be preliminarily determined to be agarwood;