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A microsporangium (pl. microsporangia) is a sporangium that produces microspores that give rise to male gametophytes when they germinate. Microsporangia occur in all vascular plants that have heterosporic life cycles, such as seed plants , spike mosses and the aquatic fern genus Azolla .
The microspore has three different types of wall layers. The outer layer is called the perispore, the next is the exospore, and the inner layer is the endospore.The perispore is the thickest of the three layers while the exospore and endospore are relatively equal in width.
A sporangium (from Late Latin, from Ancient Greek σπορά (sporá) 'seed' and ἀγγεῖον (angeîon) 'vessel'); pl.: sporangia) [1] is an enclosure in which spores are formed. [2]
Within the stamen, the microsporangium forms grains of pollen, surrounded by a protective microspore, which form the male gametophyte. Within the carpel the megasporangium form the ovules, with its protective layers in the megaspore, and the female gametophyte. Unlike the male gametophyte, which is transported in the pollen, the female ...
In a willow, microspores are not liberated from the anther (the microsporangium), but develop into pollen grains (microgametophytes) within it. The whole pollen grain is moved (e.g. by an insect or by the wind) to an ovule (megagametophyte), where a sperm is produced which moves down a pollen tube to reach the egg.
In biology, the theca of follicle can also refer to the site of androgen production in females. The theca of the spinal cord is called the thecal sac, and intrathecal injections are made there or in the subarachnoid space of the skull.
Schematic of anther (1: Filament 2: Theca 3: Connective 4: Pollen sac or Microsporangium) Section of anther, showing dehiscence and release of pollen (1: Vascular bundle 2: Epidermis 3: Fibrous layer 4: Tapetum 5: Pollen)
The unilocular gynoecium is formed by two or more united carpels and the ovules are fixed on a central column and without partitions with the ovary wall. This column may be a basal prolongation of the placenta, as in the Primulaceae , or it is the set of united placentas that persist after the dissolution of the septa, as in the Caryophyllaceae .