Question

What happens to primary phloem in stem after secondary growth?

• A. Compresses outside and degenerates
• B. Compresses inside and degenerates
• C. Becomes part of secondary phloem
• D. Modifies into sclerenchyma

Answer 1

Answer: (A)

Compresses outside and degenerates

Vascular cambium produces secondary phloem centrifugally and secondary xylem centripetally, primary phloem is pushed outward by the new cells that arise from the vascular cambium. The secondary xylem crushes the primary phloem which in turn becomes functionless and secondary phloem performs all physiological activities. Since secondary phloem crushes the primary phloem, neither it becomes part of secondary xylem nor converts into sclerenchyma
So, the correct answer is 'Compresses outside and degenerates'