I wrote earlier:

> As to the "purpose" of a cotton boll, cotton is a commercial crop of high 
> agronomic importance, and as has been said, been selectively bred for 
> certain 
> genetic traits for more than 6000 years now. In this context, to ask "what 
> purpose does the cotton boll serve the plant" is the equivalent of asking "
> what purpose does a poodle haircut serve the dog?"

Reading that paragraph over, it may have come across as harsher than I 
meant it. 

The modern cotton boll has been bred for long-staple, crystalline white, high-
density fiber, while greatly reducing the mammalian toxicity of the plant seeds, 
while simultaneously making the plant intolerant to specific commercial 
herbicides ("Round-up Ready"). None of these attributes serve the plant. 
These are qualities that only serve the human masters that grow highly 
selected cultivars, and all of these qualities would rapidly disappear if the 
plants were released to the wild again.
 
But the cotton boll does have purposeful, evolutionary value to the plant, just 
as the hair of a poodle has similar enormous value to the dog, but not in its 
human-dictated configuration, nor for any human-valued reason.

All fruits in flowering plants serve the purpose of seed dispersal, but there is 
no single, royal road to that end. Fruits can explode, fly, parachute, become 
ensnared on the coats of animals, drift on flowing streams or be eaten by 
animals as their specifically chosen method of dispersal. Whichever method is 
chosen, the phylogenetic lineage optimizes its fruits for that purpose over 
evolutionary time.

Some of these methods are shown here:

   http://www.cas.vanderbilt.edu/bioimages/pages/fruit-seed-dispersal.htm

Quite often the method of seed dispersal employed by a specific plant species 
requires the co-evolution with specific animals, and when those animals are 
locally extincted, the plants are put at risk. Look particularly at the fruit of the 
Osage orange on the page above. It's giant structure is believed to be an 
attractive adaptation to dispersal by Pleistocene megafauna (mammoths, giant 
sloths, etc.) that were killed off by the arrival of humans in North America 
13,000 years ago, and the plant is therefore at some heightened risk of long-
term survival now.

But the more important picture is this one:

http://www.hear.org/starr/hiplants/images/600max/html/starr_011104_0049_go
ssypium_tomentosum.htm

This is an image of the opened boll of a wild species of cotton in Hawaii. The 
fibrous lint, when released by the plant, will carry the plant's seeds in the 
wind, or at least along the ground, much like a dandelion's, so that the people 
who suggested that purpose were on the right track, and that's the statement 
that I wanted to correct.

Also note that the lint is brown. Wild cotton lint occurs in brown, black, red, 
green, as well as a variety of whitish yellow colors. These species have been 
banned from the fields of commercial growers simply for fear of genetically 
contaminating the very white varieties that have been bred, but color, if it has 
any selective value at all in its original context, must have been a very minor 
consideration for purposes of seed dispersal.

Wirt Atmar

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