274 BIOLOGY 



the fact that it will grow into a new plant without being 

 united with another cell. The macrospore is also proved to 



be a spore by the same fact, since it 

 also grows into a new plant without be- 

 ing fertilized. Since the flower-bear- 

 ing plant thus produces spores instead 

 of eggs and sperms, it is clearly a 

 sporophyte rather than a gametophyte, 

 and it corresponds to the fern frond 

 rather than the fern prothallium. It 

 FIG. 126. MAGNIFIED differs from the fern, however, in that 

 SECTION OF THE YOUNG it produces two kinds of spores instead 

 OVULE, o, OF A FLOWER- of one. This condition is spoken of as 

 ING PLANT heterosporous (Gr. heteros = other + 



sp, macrospore; n, its nucleus. ^^ in digtinction from the homo . 



sporous (Gr. homos = alike) condition of the fern. 



If we now try to follow out a comparison between the flower 

 and the fern, we should expect that the flower spores would 

 germinate at once into gametophytes, just as the fern spores 

 germinate into the prothallium, and that the gametophytes 

 would produce the real sex organs with sperms and eggs. Since, 

 however, there are two kinds of spores, we might expect two 

 kinds of gametophytes to grow from them instead of one kind, 

 as in the fern. This actually occurs, only the two gametophytee 

 are very small and rudimentary. The macrospore never gets 

 out of the pistil but, in the midst of the pistil tissue, develops 

 quickly into a tiny growth that represents a gametophyte 

 stage, and this soon produces what corresponds to an arche- 

 gonium with its egg; Fig, 127. All this occurs early in the 

 life of the flower, before any pollen has been brought to the 

 pistil, and consequently before fertilization can have occurred. 

 It is simply the germination of a spore to form a gametophyte. 

 The pollen, too, goes through its history, growing very slightly 

 but sufficiently, to show that it develops into a gametophyte 

 in its turn. This occurs either before it has left the anther 



