Question

Mixed protostele with example

Answer 1

Answer:

Ø Mixed protostele with pith is considered as a connecting link between protostele and siphonostele. Ø Example: Hymenophyllum demissum, Lepidodendron selaginoides. Ø A stele with pith (medulla) at the centre is called siphonostele. Ø The central core of pith is surrounded by the xylem.

Answer 2

ANSWER :-

Definition of Mixed Protostele- 

Mixed protostele is referred to the type of protostele in the case of which, xylem is present in the form of discrete units embedded in phloem.

Example of species or case where mixed protostele is found is as follows- 

• Lycopodium cernuum.

Extra Information-

• Protostele is referred to as the most primitive type of stele and all of the other kind of steles have been derived from it. -

1. In the case of this kind of stele, the pith is completely absent. 
2. This primitive type of stele is found in Lygodium, Psilotum, Selaginella, etc.

• Protostele consists of four further different types within itself. The types are as follows-

1. Haplostele- Here, solid round central core of xylem is surrounded by phloemand pericycle. Examples of species or cases where haplosteles are found are as follows- Selaginella kraussiana, Rhynia, Horneophyton, Cooksonia, etc.
2. Actinostele- Here, central xylem is star shaped with radiating arms and phloem is present in separate patches. Examples of species or cases where actinosteles are found are as follows- Asteroxylon, Lycopodium serratum, Psilotum, etc.
3. Plectostele- Here, xylem is present in the form of separate plates and phloem is present between these xylem plates. Example of species or cases where plectosteles are found are as follows- Lycopodium clavatum and Lycopodium volubile.
4. Mixed Protostele- defined in the question already.