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( Sporangium)
A sporangium (pl., sporangia) is a plant or fungal structure producing and containing spores. Sporangia occur in angiosperms, gymnosperms, ferns, fern allies, bryophytes, algae, and fungi. Their spores are sometimes called sporangiospores. On ferns, the mature plant is a sporophyte that develops sporangia, tiny, stalked sacs which contain meiospores, on all or just certain leaves (called sporophylls if sporangia are present). The spores are usually on the underside of the leaves. In mosses, the little case that rises above the vegetative growth on a thin stalk is a sporangium often called a capsule that, as in ferns, produces meiospores. This sporophytic (diploid) growth arises out of the gametophytic (haploid) archegonium after the ovum is fertilized. The sporophyte initially has some chlorophyll, but later turns brown and becomes dependent upon the gametophyte for nutrition, which is absorbed through the foot (base of the stalk), embedded in the archegonial tissues. Categorized based on developmental sequence, eusporangia and leptosporangia are differentiated in the vascular plants. In a leptosporangium, found only in ferns, development involves a single initial cell that becomes the stalk, wall, and spores within the sporangium. There are around 64 spores in a leptosporangium. In a eusporangium, characteristic of all other vascular plants and some primitive ferns, the initials are in a layer (i.e., more than one). A eusporangium is larger (hence contain more spores), and its wall is multi-layered. Although the wall may be stretched and damaged, resulting in only one cell-layer remaining.
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