JE>>     Deeper roots; varieties that have developed over time to be
  >>     resistant to drought and extremes of temperature.
 DD> ...  Doesn't the grass, which has been there
 DD> a long time, fit into the same category as the weeds...just
 DD> curious.
While I would agree that some "weeds" *have* "developed over time to be...", 
this would be true of *any* kind of plant that must endure (and survive  :) 
excessive conditions.  However, the term "weed" is, truly in the eye of the 
beholder.  Bermuda is *not* a "desired" grass in many lawns in coastal 
Alabama, however, in Texas and Oklahoma, (where I now find myself,) it is a 
lawn of choice!  I can tell you, with authority, that the roots of *this* 
"weed" (IMO  :) do. indeed, go down, sometimes as much as 16-18"... a fact 
that *anyone* who has ever tried to dig it out, (in an attempt to get *rid* 
of it!   :) will readily attest to.  Johnson grass is the same.  However, 
there is also a "weed", which many spend hundreds of dollars (each late 
winter) to get rid of, called chickweed, that is very shallow-rooted.
I might also share, that I spend hundreds of dollars each year, ingesting 
this "weed", as it is a very useful herb that those of you who find 
cholesterol to be a problem in your life, would do well to get to know!   It 
is useful for other things, as well.  I only mention this,  as cholesterol 
seems such a problem for so many  in today's society.   I, actually, don't 
take it for that reason...  taken it for years, don't *have* a cholesterol 
problem,  (which may be significant to some  :),  (don't have a chickweed 
problem, either,  :)
So, I guess what I am trying to say is, some weeds have deep root systems, 
some don't... some are easily controlled, some are not.  All "weeds"  are 
merely, plants that are growing where you don't want them to grow, as well 
as, plants that you don't know what to do with!  Tomatoes, potatoes, (neither 
of which Europeans would *touch*, )  and many other plants, started out as 
"weeds"!  I have often been thankful for that *first* adventuresome soul who 
took some 'un-educated, savage's (I'm being humorous, here  :)  suggestion, 
and tried them... and decided that they needed to be planted somewhere 
besides where they were growing... and put them in a *garden*!   :)  BTW, 
neither of these plants like to be fertilized with  high nitrogen 
fertilizer... (which most grasses don't mind at all   :)
cheers,
wls
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