Emilian Kozielski
Emilian Kozielski voted up Anonymous' answer

Do you have access to a record of that plant's ancestors?

Assuming white is recessive and purple is dominant:

With a record of that plant's ancestors you'd be able to know if that plant is a likely carrier of the recessive allele.  This would be a heterozygous punnet square.  If it was homozygous for the dominant … Read more