Question

The stem of Selaginella is anatomically characterised by the presence of
A.Siphonostele
B.Amphiphloic siphonostele
C.Protostele
D.Ectophloic siphonostele

Answer 1

Hint: The stem is commonly erect and radially con­structed in the subgenus Homoeophyllum. The species having a place with the subgenus Heterophy­llum are prostrate and dorsiventral. The branching is dichotomous in the individual from Homoeophyllum and to some degree horizontal in Heterophyllum. The life structures of the develop stem is very dis­tinct and is separated into an external epider­mis, center cortex and midway found stele.

Complete answer:
> Cross over segments of stem, anatomically, it is separated into an external layer of epidermis, center layers of cortex and midway found stele. Outermost one-celled thick epidermis comprises cutinized cells with no stomata. In the greater part of the species, the cortex is separated into a couple of external layers, of thick-walled sclerenchymatous hypodermis and numerous inward layers of slender walled parenchymatous cells, while in exceptionally fragile species it is completely made out of flimsy walled parenchymatous cells.
> Cortex is totally sclerenchymatous in xerophytic species. Generally, there is no intercellular space in the cortex. Centrally found stele (or steles) is associated with the cortex with the assistance of some long, radially extended cells called trabeculae. In between these trabeculae there are available many air holes or huge intercellular spaces. That these trabeculae are the endodermal structures is appeared by the presence of many bands like casparian strips in them. Trabeculae are missing in species like S.adunca, S. rupestris, etc.
> Structurally, a stele fluctuates from a straightforward protostele to a polycyclic siphonostele in various species. Yet, regularly it is protostelic, i.e., xylem is encircled by phloem with no pith. Each stele comprises pericycle, phloem and xylem.
> Pericycle comprises some slightly walled parenchymatous cells. Phloem comprises sieve cells and phloem parenchyma. There is no companion cell.
> Xylem is an exarch with a couple protoxylem gatherings. It consists of just tracheids.

So, the correct answer is option C.

Note: The stem of Selaginella is shaped like a vascular stele which is protostele. Xylem is available in the middle and is encircled by phloem and phloem is encircled by pericycle. Pith is missing. Trabeculae are available which are tube loved structures and are adjusted endodermal cells with casparian strips. In Selaginella, stele is polystelic. In young stems, just a single stele is available (monostelic), however developed stems are distelic or polystelic. The midway found xylem is exarch and diarch. It comprises tracheids as it were. The phloem comprises phloem parenchyma only. Trabeculae alludes to the projections from the cell wall that reach out over the cavity of the channels of specific plants. In the stem of Selaginella kraussiana, air spaces create between the two endodermal cells disengaging the steles from the cortex. The endodermal cells extend to frame trabeculae interfacing the two tissues.