The scientist can conclude that the plants that were used in this experiment contained both a dominant and recessive allele. That the plants were hybrids which causes the off springs to have a 3:1 ratio.
The scientist can conclude that both or one of the pea plant (either white or purple) has or possesses recessive alleles. Also this cross can be possibly between a heterozygous dominant and homozygous recessive pea plant. Suppose the white pea plant is homozygous recessive (ww) and the purple plant is heterozygous dominant (Pw) then the cross between the two would result into
Pw x ww
Pw, Pw, ww, ww
Thus the offsprings have both purple and white flowers.
