Question

Discuss the process of spore dispersal in Marchantia. What environmental factor stimulates the release of the spores? What are elaters? How do they function to release the spores?

Answer 1

Spore dispersal in Marchantia: (you can find answer of other question in this whole mechanism too)

In Marchantia, after fertilization the diploid zygote develops into sporogonium (having a spore-capsule) through many divisions. A mature sporogonium can be differentiated into three parts, viz., the foot, seta and capsule.

Foot: It is bulbous and multicellular. It is composed of parenchymatous cells. It acts as anchoring and absorbing organ. It absorbs the food from the adjoining gametophytic cells for the developing sporophyte.

Seta: It connects the foot and the capsule. At maturity, due to many transverse divisions it elongates and pushes the capsule through three protective layers viz., calyptra, perigynium and perichaetium.

Capsule: It is oval in shape and has a single layered wall which encloses spores and elaters. It has been estimated that as many as 3, 00,000 spores may be produced in single sporogonium and there are 128 spores in relation to one elater. As the sporogonium matures, seta elongates rapidly and pushes the capsule in the air through the protective layers. The ripe capsule wall dehisces from apex to middle by four to six irregular teeth or valves. The annular thickening in the cells of the capsule wall causes the valves to roll backward exposing the spores and elaters. The elaters are hygroscopic in nature. In dry weather they lose water and become twisted. When the atmosphere is wet, they become untwisted and cause the jerking action. Due to this the spore mass loosens and spores are carried out by air currents.

What environmental factor stimulates the release of the spores?

Changes in humidity are the major environmental factor that stimulates the release of the spores.

What are elaters? How do they function to release the spores?

Elaters and its role in spore dispersal: A tiny elongated structure that helps disperse plant spores by coiling and uncoiling in response to changes in humidity. The elaters are hygroscopic in nature. Marchantia have a characteristic method of spore dispersal. Inside the sporophyte capsule, spores are attached to specialized cells known as elaters. The elater is tubular in shape and has one or more cell wall thickenings which are helically oriented along the long axis of the cell. These helical thickenings are hydroscopic, in that they readily absorb water. In dry weather they lose water and become twisted. When the atmosphere is wet, they become untwisted and cause the jerking action. Due to this the spore mass loosens and spores are carried out by air currents.