Spores are small reproductive structures that are released from the sporangium.
Dr Leon Perrie
So a spore is the product of meiosis. In ferns, it’s tiny. If you think of a ruler and think how big a centimetre is and divide that by 10, then you've got a millimetre, and then divide that by 10 again and then halve it. That is about the size of the spore.
Video: © University of Waikato
Micrograph of spore, Australasian Pollen & Spore Atlas, Creative Commons 3.0