Heterospory involves formation of two types of spores. Microspores are smaller in size and megaspores are much larger in size. In some Pteridophytes, the microspores and megaspore germinate to give rise to male and female gametophytes respectively. Finally, the zygote develops inside the female gametophyte. From evolutionary perspective, this is a precursor of seed habit in higher plants. Seeds have  enabled gymnosperms and angiosperms to tide over long p e r i o d s  of unfavourable conditions. Seeds have also enabled them to spread to wider geographical area through seed dispersal. It has indeed helped these plants in further evolution.