Question: how are xylem and phloem arranged in protostele of selaginella?
Answer: Polystele: Generally in a protostele, the stem has a single stele in the centre. But in Selaginella, the stem axis has several steles in parallel arrangement (di-stelic or polystelic). Each stele is a protostele with xylem core surrounded by phloem with pericycle and endodermis.