Sentence Examples with the word macrospore

The male gametophyte is represented by one or few cells and, except in a few primitive forms where the male cell still retains the motile character as in the Pteridophyta, is carried passively to the macrospore in a development of the pollen grain, the pollen tube.

In the natural order Rosaceae, the series Querciflorae, and the very anomalous genus Casuarina and others, instead of a single macrospore a more or less extensive sporogenous tissue is formed, but only one cell proceeds to the formation of a functional female cell.

The ovule is not enclosed in an ovary, and the usually solitary macrospore becomes filled with a prothallus, in the upper part of which are formed several rudimentary archegonia.

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The germination of the macrospore consists in the repeated division of its nucleus to form two groups of four, one group at each end of the embryo-sac. One nucleus from each group, the polar nucleus, passes to the centre of the sac, where the two fuse to form the so-called definitive nucleus.