Question

Formation of secondary xylem and phloem respectively are
(a) Centrifugal and centripetal
(b) Centripetal and centrifugal
(c) Both centripetal
(d) Both centrifugal

Answer 1

A ring of thin-walled, non-lignified cells, which pass through the center of each vascular bundle and through the interfascicular parenchyma, forms the cambial region. The cambial region consists of the original vascular cambium, and the cambial derivatives, nearly distinct from it on either side of it.

Complete answer:
Centrifugally formed derivatives are intended to differentiate into secondary phloems, and centripetally formed derivatives are intended to differentiate into secondary phloems. Two division patterns are exhibited by vascular cambium; multiplicative divisions or additive divisions, thereby cutting more aggressively in the middle. The circumference of the vascular cambium is augmented by multiplicative divisions. Additive division adds mother cells of phloem or xylem that divide into their respective groups of cells.
In the middle of the stem, the primary xylem is developed towards the inner side, while the primary phloem is forced outward by the new cells that develop from the vascular cambium, i.e., produced towards the outer side. The trend of development that travels into the center is called centripetal, while those that move away from the center are called centrifugal. Xylem shows centripetal growth, while phloem shows a pattern of centrifugal growth.
Thus, choice (b) is the right answer i.e., Centripetal and centrifugal.

Note: Cambium cells are arranged in regular radial bands, are flattened tangentially, are thinner than radial walls, and contain cytoplasm and nuclei in the cells. You will note that the cambial cells are elongated, with chisel-shaped ends, if viewed in the longitudinal segment.