What is the purpose of a thorn?

In doing some research for a Bible-related topic, I started wondering just what the purpose of a thorn is? Protection? If so, against what? What is a thorn comprised of? Why do some plants (flowers) have them and others do not? Anything and everything would be great.

As for the Bible topic, it's about "prayer". I'm teaching a ladies Bible class on Wednesday nights and we're focusing on Fellowship with the Father. I read something about how we're quick to thank God for the flowers, but don't realize that we learn a whole lot more from the thorns. Thus, we should thank Him for the thorns, too. Before I use this in a classroom setting, I'd like to know a little more about the purpose of thorns in the botanical sense.

Thanks in advance.

A thorn is a modified stem and is most often utilised for protection against browsing animals who might otherwise find the plant rather tasty. They don't prevent the smaller mammals and birds who are the normal carriers of their seeds to other places.

Other plants have developed different types of protection, often this suits the kind of pests the species is trying to put off. Alliums, for example, have a strong smell, this helps put off many pests and while it doesn't prevent them from being eaten, they aren't eaten in quantities large enough to rid an area of them. Other plants have evolved a very fast reproduction cycle in another attempt at survival. There are so many different ways plants have developed to try and keep the usual pests away.

Survival is always the key word for any living thing. It shouldn't be forgotten that while this self protection seems entirely selfish, plants can also help others to grow less molested than usual and it can work to the benefit of both species.

Of course, many living things may also use thorns (and other plant protections), humans have made needles from them (ok and weapons but that just shows you how inventive we really are, that's the positive way of thinking about it), other animals and insects use a plants' protection for their own too. Anyone remember Brer Rabbit in the Briar Patch? Bo the dog will also roll in anything with a strong smell to disguise his smell because he thinks we're off hunting. It's all part of the great balance of living things.

This message was edited Jan 11, 2004 7:38 PM

That is truly enlightening, Baa. Some animals have horns, and some plants have thorns!

Carla, my books are packed but I seem to remember Antoine de Saint-Exupéry, in The Little Prince, had something pithy to say about thorns on roses. It's been years since I have re-read it thoroughly and I may be wrong. The Little Prince's relationship with his rose is quite interesting in the book.

Thank you Dinu. I'm always fascinated by how plants and animals have manipulated their situations to survive.

certain plants develop thorns as a means of climbing

A lot of plants that live in the desert have thorns. That is because life in the desert is hard enough without having animals munching on you. They say that the spines of a cactus, besides providing protection from grazers, may also provide some shade and reduce the speed of drying winds.

The spines on cholla cactus allow the joints to stick to the fur of passing animals and then the joint is deposited elsewhere where it may root and grow a new plant. Most chollas don't reproduce by seed very well.

This is a picture of a silver cholla, which looks very well proctected and shaded.

Kelli, I have been told that many of the cactus spines are actually tightly rolled leaves that collect the precious moisture available to them...much more efficient than a flat leaf in the heat of day. Could this be true?

I don't really know, Weez. I think that cactus thorns, leaves (for the few kinds that have leaves, either permanantly or temporarily), and flowers all grow from the areoles. A cactus spine is a different structure than the thorn of a woody plant, but I don't know the details.

As for catching moisture, that is probably true, though I don't know how much dew they get in the desert. I friend of mine who lived in Tucson said that they "never" got dew. That process probably works well in coastal places, though. My observation has been that cacti can only live where there is year-round rain - not a lot of rain, of course, but not extended absolutely rainless periods. The deserts of the American southwest get some winter rain and some summer rain. Where I live, which is not considered desert, we only get rain in the winter and will go for five months in the hottest part of the year without rain. The only places that cacti grow in the wild here are places that get a lot of ocean influence (fog and cooler air).

When I was told that the spines are leaves, I began noticing some of my house cactuses (cacti?). When I watered them as regularly as the other plants, they sprouted little bunny ears. I wondered if these were unfurling spines.

Here's some info on Cactus spines. No mention of curled leaves...must have been bunk:

What good are cactus spines?
Cactus spines didn't evolve to punish clumsy hikers. Their chief function, as one might expect, is to protect cacti from hungry animals. It doesn't always work. Javelina devour entire prickly pear pads, spines and all, and thirsty jackrabbits and cottontails nibble carefully between the areoles. Spines may offer little impediment to cactus-consuming bugs and beetles, though flying insects occasionally blunder into them, impaling themselves helplessly on the tips.
Spines of some of the more densely-cloaked cacti collectively shade the plants from overheating and sunburn, and the thick mat of spines at the growing tip of a saguaro or barrel cactus provides insulation against freezing on clear winter nights. A cholla segment that affixes itself by means of its spines to a passing deer or hiker serves a reproductive purpose: it may eventually sprout roots after being disengaged some distance away.

Animals sometimes turn cactus spines to their own advantage. Packrats pile the fiercely spined joints of chollas around their dens, discouraging predators. Certain birds seem to nest in spiny chollas for similar reasons, but must protect their own nestlings from the hazard. Cactus wren nestlings are safe inside covered nests, while curve-billed thrasher parents systematically break off the tips of spines near their nest cups. Mummified snakes are sometimes found entangled in cholla spines--the aftermath of failed nest raids.

Even human beings have found uses for cactus spines. Native people have fashioned sewing needles from them, and used curved barrel cactus spines as fish hooks. A stout prickly pear spine (with the tip snapped off) makes a fine toothpick, and cactus spines were once sold as record playing needles for wind-up Victrolas!

Thanks, everyone. This has been very interesting to read. I knew you all would be able to help me.

Do you think that the rose or flowers would be a good thing and the thorns a bad thing, like a saying i have heard you got to take the good with the bad, because they stick you. My preacher did a sermon about this, one sundaay. that people think Oh why is God doing or letting this bad thing happen to me. but If we didn't have the bad or low points we wouldn't appreciate the good things and Blessings we have in our lifes.

WZ

Your information is right, spines in the true sense (including those on cacti) are modified leaves.

Thanks, Baa. My faith is restored in 'Whitey' the old man with the platter sized hand who played pool at the bar at which I worked. He used to impart bits of wisdom as he dropped balls into the pockets. One pearl of wisdom was was concerning the spines of a cactus. Whitey is long since dead, but his wisdom live on!

Isn't there something about being thankful that thorns have roses?