When plants of $$F_1$$ generation are allowed to reproduce without a cross, the alleles segregate and one allele goes to one parent while another allele goes to another parent. This is in accordance with the transfer of a halved number of the chromosome during meiosis. This segregation is a random process and there is a 50% chance of a particular allele going to either the male gamete or the female gamete. Due to this, the genotype produced in $$F_2$$ generation is the same as the phenotype produce in that generation. So, the percentage of plants with pure genotype and those with mixed genotype will be the same, i.e. 50%.