Subject: Can the roots of plants utilize CO2?

I was wondering if any other part of the plant besides the 
leaves can utilize carbon dioxide...specifically can CO2 
dissolved in water be utilized by the root system?  A friend of 
mine brought in an ad claiming that the addition of CO2 tablets 
to the water source for plants would increase the rate of growth 
by a substantial margin by providing more CO2 to the plant 
through the roots.  I am under the impression that only O2 is 
utilized by the roots and CO2 by the leaves.  As a matter of 
fact, I've heard some say that excessive CO2 around the roots 
will cause an anaerobic condition that can lead to root/plant 
death.  

Thanks in advance...I've been searching for an answer everywhere 
so I hope you can help me discover if these CO2 tablets really 
get results or are they a con.

NB

Re: Can the roots of plants utilize CO2?