Biology Lab Review - Plants

Part 2 - Seedless vascular plants - Fern

Photos by Dr. Rob Bowker, Glendale Community College, Glendale, Arizona
(These photos are protected by copyright and may not be reproduced without written permission.)

 This is a photo of a fairly typical fern plant in its natural habitat. 
  • Note that each leaf (frond) is subdivided into smaller leaflets.  This is true of most ferns.
  • The fern in the photo below has leaves subdivided in a different way.  Leaves of each different fern species have their own unique form.
  • This leafy plant grew from a fertilized egg.  The pictures below show different parts of the fern's sexual life cycle.

Here is another type of fern, one whose leaves are not as finely divided as in the species in the photo above.
  • Note the curled tips of the fronds.  Very young leaves are curled up like the end of a violin and are called "fiddleheads."  These have uncurled almost all the way.
  • The sori on the leaves of this type of fern are shown below.

 This photo shows the underside of a fern leaf, enlarged so you can see the sori.
  • One sorus (A) looks like a brown spot on the leaf.
  • Viewed through a microscope (see below), you can see that a single sorus is actually a complex structure.

This photo shows a slice through a sorus on a fern leaf, as seen through a microscope.
  • You can see the cells in the fern leaf (A).
  • You can see the indusium (B) that protects the sorus while it is developing.  B falls off when the spores are ready for release.
  • When a sorus looks brown and crumbly, B is gone and you are seeing the exposed spore containers (sporangia) (C), ready to pop open and release the spores contained inside..
  • You can see more than a dozen sporangia in this photo, each containing spores.
  • Each spore is a single cell that is capable of dividing if it lands in a moist, protected spot.  By cell division, it grows into the prothallium shown below.

This photo shows a prothallus (=prothallium) that grew from a single fern spore.
  • It is tiny and fragile, only about 1-3 millimeters across. 
  • It is visible with the naked eye, but a microscope is required to see the sex organs on its surface.
  • The dark area in the center is where tiny sex organs grow, male structures that produce sperm and female structures that produce egg cells.
  • When the prothallus is flooded with water, sperm swim to eggs and fertilization occurs. (Usually male and female parts don't mature at the same time on one prothallus, so the sperm must swim to another one nearby.)

This photo shows a fern embryo growing from a prothallus.  (There weren't very many slides of this advanced stage in the lab.  Most of them showed only a lump of cells on the prothallus, the earliest stage of embryo growth.)
  • B is the structure shown in the photo above, now dying, it's function accomplished.
  • A is the fern embryo, which is growing from a fertilized egg.  The embryo extends from the leaf (marked A) all the way down to the dark root going off to the left at the bottom of the photo.
  • This embryo will grow into the large fern plant, like those shown in the photos at the top of the page.

Go to part 1 (Moss)
Go to part 3 (Conifer)
Go to part 4 (Flowering plant)
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