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megaspores's Usage Examples:

and contain either an im The upper sporangia contain numermense number of minute ous microspores; in each of the lower spores or a very small number sporangia four megaspores are shown.

The fructification consists of long, lax spikes, with whorled sporophylls; indications of megaspores have been detected in the sporangia.

The megaspores, of which there are many in the megasporangium, have a diameter about three times that of the microspores.

It has recently been stated, however, that the supposed Algae are in reality the megaspores of Vascular Cryptogams. Scarcely anything is known of Palaeozoic Florideae; Solenopora, ranging from the Ordovician to the Jurassic, resembles, in the structure of its thallus, with definite zones of growth, Corallinaceae such as Lithothamnion, and may probably be of the same nature.

The microspores are united by means of hardened protoplasm into one or more masses, while the solitary megaspores have a more or less complicated episporium.

In the megasporangium, on the other hand, the four megaspores, which arise from a single mother-cell, are nourished at the expense of the other sporogenous cells and of the tapetum.

Some Calamites were heterosporous, sporangia with microspores and megaspores being found in the same cone.

The spores produced in each sporangium vary from very many to a single one in the case of some heterosporous forms. These latter bear spores of two kinds, microspores and megaspores, in separate sporangia.

It has been shown by Lawson that in Sequoia sempervirens (Annals of Botany, 1904) and by other workers in the genera that several megaspores may attain a fairly large size in one prothallus.

These, as in Gymnosperms, are of two kinds, microspores or pollen-grains, borne in the stamens (or microsporophylls) and megaspores, in which the egg-cell is developed, contained in the ovule, which is borne enclosed in the carpel (or megasporophyll).

megaspores's Meaning':

larger of the two types of spore produced in heterosporous plants; develops in ovule into a female gametophyte