Q.What is the fate of primary xylem in a dicot stem showing extensive secondary growth?

Extensive secondary growth crushes the primary xylem, which lies helplessly at the very centre of the mature axis.

Secondary growth in a dicot stem is driven by the vascular cambium, a lateral meristem that forms a continuous ring between the primary xylem and primary phloem. Every growing season, the cambium cuts off new secondary xylem towards the inside and secondary phloem towards the outside. Because secondary xylem accumulates in enormous quantity over years (this is what becomes 'wood'), the vascular cambium ring, along with everything outside it, keeps getting pushed further and further outward.

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