The alleles of the genes for height will control the height in each plant. As we can infer from the description in the question, the alleles for the tall trait will be dominant over the alleles of the recessive trait. This is the reason that all the F1 offsprings were observed to be tall. However, the results of the F2 generation interpret that most of the F1 generation plants were heterozygous dominant. When heterozygous dominant plants are crossed, there will be a sound chance for the recessive trait to occur in the F2 generation.