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How does the vascular cambium produce new xylem and phloem?

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fern life cycle — Plant development The life cycle of the fern. (1) Clusters (sori) of sporangia (spore cases) grow on the undersurface of mature fern leaves. (2) Released from its spore case, the haploid spore is carried to the ground, where it germinates into a tiny, usually heart-shaped, gametophyte (gamete-producing structure), anchored to the ground by rhizoids (rootlike projections). (3) Under moist conditions, mature sperm are released from the antheridia and swim to the egg-producing archegonia that have formed on the gametophyte's lower surface. (4) When fertilization occurs, a zygote forms and develops into an embryo within the archegonium. (5) The embryo eventually grows larger than the gametophyte and becomes a sporophyte.

The vascular cambium is a lateral meristem responsible for the secondary growth—or thickening—of plant stems and roots. It originates from undifferentiated procambium cells that persist between the primary xylem and primary phloem.123

The cambium functions through the activity of two types of initial cells:
* Fusiform initials: Elongated cells that produce the vertical (axial) system of secondary xylem and phloem.34
* Ray initials: Isodiametric cells that produce vascular rays, which form the horizontal system for food and water storage and translocation.34

These cells divide in a plane tangential to the stem's surface, generating xylem mother cells toward the inside and phloem mother cells toward the outside. These mother cells continue to divide, adding new layers of tissue. Because the cambium produces more cells internally than externally, significantly more secondary xylem is created than secondary phloem. As the stem increases in girth, the cambium also undergoes radial divisions to expand its own circumference, ensuring it keeps pace with the growing plant.32