Title: Phloem
Content:  Phloem is produced in phases. Primary phloem is laid down by the apical meristem and develops from the procambium. Secondary phloem is laid down by the vascular cambium to the inside of the established layer(s) of phloem. In some eudicot families (Apocynaceae, Convolvulaceae, Cucurbitaceae, Solanaceae, Myrtaceae, Asteraceae, Thymelaeaceae), phloem also develops on the inner side of the vascular cambium; in this case, a distinction between external and internal or intraxylary phloem is made. Internal phloem is mostly primary, and begins differentiation later than the external phloem and protoxylem, though it is not without exceptions. In some other families (Amaranthaceae, Nyctaginaceae, Salvadoraceae), the cambium also periodically forms inward strands or layers of phloem, embedded in the xylem: Such phloem strands are called included or interxylary phloem.
Title: Vascular cambium
Content: Fusiform initials (tall, axially oriented) ; Ray initials (smaller and round to angular in shape) The cambium present between primary xylem and primary phloem is called the fascicular cambium (within vascular bundles). During secondary growth, cells of medullary rays, in a line (as seen in section; in three dimensions, it is a sheet) between neighbouring vascular bundles, become meristematic and form new interfascicular cambium (between vascular bundles). The fascicular and interfascicular cambia thus join up to form a ring (in three dimensions, a tube) which separates the primary xylem and primary phloem, the cambium ring. The vascular cambium produces secondary xylem on the inside of the ring, and secondary phloem on the outside, pushing the primary xylem and phloem apart. The vascular cambium usually consists of two types of cells:
Title: Xylem
Content:  root, and the xylem develops from the inside outwards towards the periphery, i.e. centrifugally. The protoxylem is thus closest to the center of the stem or root and the metaxylem closest to the periphery. The stems of seed plants typically have endarch development. ; Mesarch is used when there is more than one strand of primary xylem in a stem or root, and the xylem develops from the middle of a strand in both directions. The metaxylem is thus on both the peripheral and central sides of the strand with the protoxylem between the metaxylem (possibly surrounded by it). The leaves and stems of many ferns have mesarch development. There are four main patterns to the arrangement of protoxylem and metaxylem in stems and roots.  The other three terms are used where there is more than one strand of primary xylem. 
Title: Root
Content:  potato have secondary growth but are not woody. Secondary growth occurs at the lateral meristems, namely the vascular cambium and cork cambium. The former forms secondary xylem and secondary phloem, while the latter forms the periderm. In plants with secondary growth, the vascular cambium, originating between the xylem and the phloem, forms a cylinder of tissue along the stem and root. The vascular cambium forms new cells on both the inside and outside of the cambium cylinder, with those on the inside forming secondary xylem cells, and those on the outside forming secondary phloem cells. As secondary xylem accumulates, the "girth" (lateral dimensions) of the stem and root increases. As a result, tissues beyond the secondary phloem 
Title: Bark (botany)
Content:  and the vascular cambium, are the only parts of a woody stem where cell division occurs; undifferentiated cells in the vascular cambium divide rapidly to produce secondary xylem to the inside and secondary phloem to the outside. Phloem is a nutrient-conducting tissue composed of sieve tubes or sieve cells mixed with parenchyma and fibers. The cortex is the primary tissue of stems and roots. In stems the cortex is between the epidermis layer and the phloem, in roots the inner layer is not phloem but the pericycle. From the outside to the inside of a mature woody stem, the layers include the following:   In young stems, which lack what is 
Title: Meristem
Content: Vascular cambium, which produces secondary xylem and secondary phloem. This is a process that may continue throughout the life of the plant. This is what gives rise to wood in plants. Such plants are called arboraceous. This does not occur in plants that do not go through secondary growth (known as herbaceous plants). ; Cork cambium, which gives rise to the periderm, which replaces the epidermis. There are two types of secondary meristems, these are also called the lateral meristems because they surround the established stem of a plant and cause it to grow laterally (i.e., larger in diameter).
Title: Xylem
Content:  As a young vascular plant grows, one or more strands of primary xylem form in its stems and roots. The first xylem to develop is called 'protoxylem'. In appearance protoxylem is usually distinguished by narrower vessels formed of smaller cells. Some of these cells have walls which contain thickenings in the form of rings or helices. Functionally, protoxylem can extend: the cells are able to grow in size and develop while a stem or root is elongating. Later, 'metaxylem' develops in the strands of xylem. Metaxylem vessels and cells are usually larger; the cells have thickenings which are typically either in the form of ladderlike transverse bars (scalariform) or continuous sheets except for holes or pits (pitted). Functionally, metaxylem completes its development after elongation ceases when the cells no longer need to grow in size.
Title: Xylem
Content: in vascular bundles, present in non-woody plants and non-woody parts of woody plants ; in secondary xylem, laid down by a meristem called the vascular cambium in woody plants ; as part of a stelar arrangement not divided into bundles, as in many ferns. The most distinctive xylem cells are the long tracheary elements that transport water. Tracheids and vessel elements are distinguished by their shape; vessel elements are shorter, and are connected together into long tubes that are called vessels. Xylem also contains two other cell types: parenchyma and fibers. Xylem can be found: In transitional stages of plants with secondary growth, the first two categories are not mutually exclusive, although usually a vascular bundle will contain primary xylem only. The branching pattern exhibited by xylem follows Murray's law.
Title: Phloem
Content:  When the plant is an embryo, vascular tissue emerges from procambium tissue, which is at the center of the embryo. Protophloem itself appears in the mid-vein extending into the cotyledonary node, which constitutes the first appearance of a leaf in angiosperms, where it forms continuous strands. The hormone auxin, transported by the protein PIN1 is responsible for the growth of those protophloem strands, signaling the final identity of those tissues. SHORTROOT(SHR), and microRNA165/166 also participate in that process, while Callose Synthase 3(CALS3), inhibits the locations where SHORTROOT(SHR), and microRNA165 can go. In the embryo, root phloem develops independently in the upper hypocotyl, which lies between the embryonic root, and the cotyledon. In an adult, the phloem originates, and grows outwards from, meristematic cells in the vascular 
Title: Xylem
Content: 1) conifers (Coniferae): there are approximately 600 known species of conifers. All species have secondary xylem, which is relatively uniform in structure throughout this group. Many conifers become tall trees: the secondary xylem of such trees is used and marketed as softwood. ; 2) angiosperms (Angiospermae): there are approximately 250,000 known species of angiosperms. Within this group secondary xylem is rare in the monocots. Many non-monocot angiosperms become trees, and the secondary xylem of these is used and marketed as hardwood. Primary xylem is formed during primary growth from procambium. It includes protoxylem and metaxylem. Metaxylem develops after the protoxylem but before secondary xylem. Metaxylem has wider vessels and tracheids than protoxylem. Secondary xylem is formed during secondary growth from vascular cambium. Although secondary xylem is also found in members of the gymnosperm groups Gnetophyta and Ginkgophyta and to a lesser extent in members of the Cycadophyta, the two main groups in which secondary xylem can be found are:

Question: where do secondary xylem and phloem cells arise from?
Answer: The vascular cambium.
the vascular cambium.