Megaspore


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Related to Megaspore: megagametophyte, generative cell

megaspore

[′meg·ə‚spȯr]
(botany)

Megaspore

 

a spore from which develops the female prothallium (in gymnosperms, the primary endosperm nucleus; in angiosperms, the embryo sac). The megaspore arises as a result of the division of the megasporocyte (mother cell). In Pteridophyta the number of mature megaspores in the megasporangium varies. The Isoetes have many megaspores. The Lepidodendron and Sigillaria have eight to 16; the Selaginella, two to four; the water ferns, only one. Megaspores grow into female prothallia either inside (Lepidodendron, Selaginella, Salvinia) or outside (Marsilea, some Selaginella) the megasporangium. The first stages in the development of the prothallium occur inside the megaspore; the membranes of the megaspore then open and the parts of the prothallium that bear the archegonia emerge (in Salvinia they turn green). In seed plants, four megaspores usually form in each nucellus (the central part of the ovule).

References in periodicals archive ?
The megaspore diameters were obtained through the program ImageJ.
Diploids exhibit the smallest average megaspore size range (rarely over 450 [micro]m).
The small size of the mature plants and the granulate to rugulate texture of the megaspores clearly distinguished Rosenthal's collections from all other known species in northeastern North America.
Following this taxonomy, all plants examined were Azolla cristata, on the basis of the presence of bicelled trichomes, hook shaped, multiseptate glochidia, and a 3-float megaspore apparatus with a granular perine surface (Figs.
A relationship between the surface feature of the microspore and that of the megaspore has been suggested (e.
Sporophyte production was rapid, resulting in 100% and 99% emergence from megaspores from plants A and B, respectively, within the fourth week.
Masses of megaspores and microspores can be collected from pots of S.
Each megaspore contains a small colony of Anabaena azollae filaments bearing akinetes.
4 <9 width (mm) Megaspore tuberculate tuberculate ornamentation (globular (numerous large globular small tubercles) tubercles) Megaspore 595.
For description and nomenclature of megaspores and microspores we followed Hickey (1986) and Musselman (2003), respectively.
Megaspore ornamentation in both species varies from tuberculate to rugulate, but the species differ dramatically in megaspore size: Isoetes weberi spores have a mean of 356 [micro]m and a range of 220 to 450 pm; those of L maxima range from 525 to 650 pm with a mean of 583 [micro]m.
3 mm wide Microspores Laevigate Sparsely to densely echinate Megaspores size 750:630-870 [micro]m 595:460-750 [micro]m Mean: range Megaspore Densely and Ruglulate to low ornamentation distinctly and sparsely reticulate; the reticulate; the muri generally as muri low, much tall or taller lower than the than the diameter diameter of the of the included included areole areole Megaspore girdle Absent Weakly differentiated to distinctly smooth