What is protostele? Explain its types.

Explanation

In protostele xylem surrounds phloem.
The type includes Haplostele, Actinostele, Plectostele and mixed protostele.
(i) Haplostele: Xylem surrounded by phloem is known as haplostele. E.g. Selaginella.
(ii) Actinostele: Star shaped xylem core is surrounded by phloem is known as actinostele. E.g. Lycopodium serratum
(iii) Plectostele: Xylem plates altermates with phloem plates. E.g. Lycopodium clavatum.
(iv) Mixed prototostele: Xylem groups uniformly scattered in the phlocm. E.g. Lycopodium cermuum.