Microsporangia
Encyclopedia
Microsporangium is a sporangium
that produces spores that give rise to male gametophyte
s. Microsporangia are notable in spikemoss
es, and a minority of fern
s. In Gymnosperms and Angiosperms (Flowering plants), the microsporangium produce the microsporocyte, also known as the microspore mother cell, which then creates four microspores through meiosis. The microspores divide to create pollen grains. The term is not used for Bryophytes.
Development of pollen sacs begins with the differentiation of archesporial cells in the hypodermal region below epidermis at four corners of the young anther. The archesporial cell divide by periclinal division to give a subepidermal primary parietal layer and a primary sporogenous layer. The cells of the primary parietal layer divide by successive periclinal and anticlinal divisions to form concentric layers of pollen sac wall. The wall layers from periphery to centre consist of:
Sporangium
A sporangium is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. All plants, fungi, and many other lineages form sporangia at some point in their life cycle...
that produces spores that give rise to male gametophyte
Gametophyte
A gametophyte is the haploid, multicellular phase of plants and algae that undergo alternation of generations, with each of its cells containing only a single set of chromosomes....
s. Microsporangia are notable in spikemoss
Spikemoss
Selaginella is a genus of plants in the family Selaginellaceae, the spikemosses. Many workers still place the Selaginellales in the class Lycopodiopsida . This group of plants has for years been included in what, for convenience, was called "fern allies". S...
es, and a minority of fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s. In Gymnosperms and Angiosperms (Flowering plants), the microsporangium produce the microsporocyte, also known as the microspore mother cell, which then creates four microspores through meiosis. The microspores divide to create pollen grains. The term is not used for Bryophytes.
Development of Pollen Sacs
A very young anther consists of actively dividing meristamatic cells surrounded by a layer of epidermis. It then becomes two lobed. Each anther lobe develops two pollen sacs. Thus, a bilobed anther develops four pollen sacs situated at four corners of the anther.Development of pollen sacs begins with the differentiation of archesporial cells in the hypodermal region below epidermis at four corners of the young anther. The archesporial cell divide by periclinal division to give a subepidermal primary parietal layer and a primary sporogenous layer. The cells of the primary parietal layer divide by successive periclinal and anticlinal divisions to form concentric layers of pollen sac wall. The wall layers from periphery to centre consist of:
- A single layer of epidermetween which becomes stretched and shrivels off at maturity
- A single layer of endothecium. The cells of endothecium possess fibrous thickenings. They remain thin walled and constitute stomium (line of dehiscence) in the shallow groove in between the two microsporangia of the anther lobe
- One to three middle layers. cells of these layer generally disintegrate in the mature anther
- A single layer of tapetum. The tapetal cells may be uni-, bi- or multinucleate and possess dense cytoplasm. The cells of primary sporogenous layer divide further and give rise to diploid sporogenous tissue.