How can you tell which trait is controlled by a dominant and recessive allele using punnett squares?

I'd like to answer ur question.. But I dont understand it exactly.. What do ur diagrams mean? >>
W W | W w

w Ww Ww | W WW Ww

w Ww Ww | w Ww ww
??

In this case you are only dealing with one trait, the color of the flower, so each offspring should contain one allele from the mother plant and one allele from the father, not both. You're punnett square is incorrect. A plant containing the Genotype WW would only be able to produce W alleles while a plant with the genotype Ww would be able to produce either W or w alleles. The first plant (the WW) will always supply a W allele (white) to the offspring, while the second parent could supply either. You're offspring will be 50% WW (white) and 50% Ww (white).

Parent one's alleles are vertical and parent two's are horizontal.
                   W      w      
        W      WW | Ww
        W      WW | Ww

Traditionally, dominant alleles are written with a capital letter... like "W" while recessive alleles are written as lower case "w".  In fact, I always tell my students to use block letters for the dominant allele, and use lower case script for the recessive allele, so you don't confuse the size of the letters.

You can't tell dominant and recessive from the Punnett square itself.  It has to be interpreted.