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1. The outermost layer of the wall of certain spores.
2. An asexual spore developed externally by budding, as from a sporophore.


(Botany) the outer layer of the spores of some algae and fungi
ˌexoˈsporous adj


(ˈɛk səˌspɔr, -ˌspoʊr)

the outer coat of a spore.
ex`o•spor′ous, adj.
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References in periodicals archive ?
The marginal processes were flat to rounded-verrucate, ornamented with echinate and papillate projections and the exospore was smooth (Fig.
Mature spores have a dense exospore coat, a pale endospore, and single rows of 8-11 polar tubule coils (Figure 2, panels B, C).
3 cm, similar to lateral pinnae, with 1-2 basal lobules; rachis and costae stramineous to light brown, sparsely scaly, scales similar to rhizome scales; laminar tissue glabrous; veins reticulate, forming 2-3 series of areoles between costa and margin; sori round, located in (1-) 2 lines between costa and margin; sporangia glabrous; spores 47-51 x 28-38 pm, bilateral, ellipsoidal, convex to slightly concave-convex, exospore prominently verrucate, verrucae 3-6.
4 urn in length and were characterized by an outer electron-dense exospore and a thick electron-lucent endospore.
Mature spores have a two-layered wall, with both perispore and exospore, and their protoplast is fulfilled with lipid drops (Tryon and Lugardon, 1991).
The outer exospore is then covered by the perispore.
volubilis was described by Tryon and Lugardon (1991) as papillate-rugulate, with scattered spherules on the surface and in section with a plain exospore and a laminate perispore.
These changes are: #20, quadriseriate branching of axes/leaves absent [right arrow] throughout; #28, stele with radiating arms of xylem absent [right arrow] as rounded lobes; #41, radial axis/rachis trace round-elliptical [right arrow] lobed; #46, position of protoxylem in rachis/axis toward no face [right arrow] toward several faces; and #88, exospore surface nearly smooth or plain [right arrow] obviously sculptured.