REPRODUCTION IN PLANTS 



95 



portance since the cells of intermediate size may have either 

 two or four. Nevertheless the behavior of the spores of dif- 

 ferent sizes is characteristic and significant. The largest 

 spores soon settle down and, attaching themselves by the 

 flagellated end, begin to develop into new filaments. The 

 spores intermediate in size likewise form new individuals, 



FIG. 49. Ulothrix, a filamentous Green Alga. A, modified cell for attach- 

 ment at the base of a filament. B, cells of a filament which have formed 

 spores. From three cells the spores have been liberated. C, part of a filament 

 liberating spores (below), and gametes (above) which pair to form zygotea. 

 (From Coulter.) 



but the process is much less rapid; while the smallest spores 

 not only germinate very slowly, but give rise to dwarf fila- 

 ments with vigor below the normal. As a matter of fact very 

 few of the smallest spores germinate at all. Instead, they 

 unite in pairs, each pair fusing to form a large single cell. It 

 is apparent that the small spores by fusing, instead of feebly 

 germinating, perform the sex act and, therefore, are gametes, 

 while the product of this process of fertilization is a zygote. 



