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[This information was originally produced by Beverly Skinner, wildlife biologist at Innoko
National Wildlife Refuge (in west central Alaska), for radio broadcast on Public Radio stations
Students of all ages are always intrigued by the odd swellings that show up on some plant
leaves. These bumps come in various shapes from round to spindle-shaped. Their textures can
also vary. They can be smooth or sticky, hairy, fluffy, scaly, or bumpy. Next time you find one
of these little bumps, look closely at it. What you may have found is a plant gall. What exactly
is a gall and why do some plants have them?
A gall is actually an abnormal growth of plant tissue along the lines of a plant cancer. The plant
cells in that area have either become larger or have increased in numbers. A plant produces a
gall when it is stimulated to by some kind of outside substance. Often times, that outside
substance comes from an insect.
Scientists haven't figured out the entire gall chemical sequence yet but it appears that a
substance is injected into the plant by a mother insect when she lays her eggs. This chemical
causes the starch within the plant to convert to sugar which stimulates the plant cells to begin
forming a gall. When the insect eggs hatch, the young insect larvae secret the same kind of
chemical. As the young insects begin to either eat the plant or burrow into the plant for
protection they continue to stimulate the growth of the gall.
Usually the presence of a gall does not harm the host plant. The insects are dependant on the
plant for survival so it wouldn't do the insect much good if they end up hurting the plant. Each
gall making insect produces a specific kind of gall and usually it will only grow on just one
species of plant.
Galls aren't just found on leaves either. They can also be on stems, flower heads, and roots.
They only occur when the plant is growing, though, which explains why most galls are formed in the spring.
For Alaska Naturally and the Innoko NWR, this is Beverly Skinner. The natural world is full of
interesting and unique inter-relationships such as the insect gall/plant relationship. Next time
you are out among the plants, take some time to look at these gall habitats the insects have
created for themselves.
Note: This is the MapCruzin.com archive of the FWS Arctic National Wildlife Refuge website. In December, 2001 FWS took this website offline, making it unavailable to the public. It includes 90 plus pages of information and many maps. As of 2006 the important information contained in this, the original "unsanitized" version of the FWS website, has yet to return to the internet, so we will continue to maintain it here as a permanent archive to help inform activists and concerned citizens. If you find any broken links, please report them to me at firstname.lastname@example.org and I will attempt to make the repairs. January, 2008 update - A small part of the original information that was present in 2001 has made it back into the current ANWR website. There is also an archive that contains a small amount of the original information, but it is not readily available from the main website.
U.S. Fish and Wildlife Service. 2001. Potential impacts of proposed oil and gas
development on the Arctic Refuge’s
coastal plain: Historical overview and
issues of concern. Web page of the Arctic National
17 January 2001. http://arctic.fws.gov/issues1.html
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