Why do you have tubular cell sieves

Is pith a basic fabric with no special function?

the forest ecologist

Short answer: it's not the biggest question.

Long answer:

So there are three primary tissues in a plant: ground tissue, skin tissue, and vascular tissue. See below how to sort them out:

However, some sources refer to the tissue of plants in slightly different ways, indicating that the three basic tissue types are parenchyma, collenchyma, and Schlerenchyma.

  • Example: "Botany: A Laboratory Handbook" by Pfluger 2014:

    The three basic tissues of plants are parenchyma, collenchyme and sclerchyme

Since these are all "ground" tissues, this approach to classifying plant tissues would suggest that all Plant parts are made up of some type of ground tissue (including any plant parts you mention in your post). In fact, this is often the case ...

  • Again from Pfluger 2014:

    They [parenchyma] occur in practically every part of the plant and are the most common cell type in a plant.

Of the parts you mention, Xylem "specializes" in moving water through the plant via tracheids, pits, and vascular elements. Phloem moves sugar / juice through sieve tube cells, which are carried by accompanying cells; Cambium acts in the secondary growth of wood and bark via the vascular and cork cambia; and bark is a waterproof protective layer.

However, "marrow" is simply the central parenchymal cells in the stem and is therefore mainly only used for storage like "all non-specialized" basic tissue.

As for cambium: from here:

Interfascicular cambium differs from parenchymal or collenchymal cells, which are located between the vascular bundles (mainly in the trunk).