The Spore the Merrier

What am I looking at?

This image shows the spores of a small tropical fern, Ceratopteris richardii, specifically a patented strain known as the “C-Fern”. The spores are the grooved ovals in blue/purple (1). The sporangia are the larger grooved sacs that contain the spores (2). The network of tube-like structures on the left side of the image is the leaf, or frond tissue, that creates a structure called a sorus, which contains the sporangia (3). This image was depth color-coded, meaning that warmer colors, such as red and orange, are closer to the viewer and cooler colors, such as blue and purple, are farther from the viewer.  

Biology in the background

Ferns have a life cycle that involves two distinct, alternating generations. The spores released by the sporophyte – the asexually reproducing form that we commonly recognize as a fern – germinate into either a tiny, heart-shaped, hermaphroditic gametophyte (“hermaphroditic” means it has both male and female reproductive parts) or an even smaller, oval, purely male gametophyte.  

The male organs, called antheridia, produce motile, ciliated sperm, and the female organs produce eggs. Fertilization requires the presence of water – which is why you don’t usually find ferns in dry places. The sperm find eggs by following chemical signals, and upon contact, the two gametes form a zygote that develops into an embryo within the archegonium, the female sex organ. The embryo eventually develops into a sporophyte, while the gametophyte usually atrophies and dies.

The sorus of C-fern can be up to 1.5 millimeters in diameter, or roughly 20 times the width of a human hair. A single spore is a little under 100 micrometers across, or a bit larger than the width of a human hair.

Technique

These images were created using confocal microscopy.