In a monohybrid cross between tall pea plants (TT) and short pea plants (tt), a scientist obtained only tall pea plants (Tt) in the F1 generation. However, on selfing the F1 generation pea plants, he obtained both tall and short plants in the F2 generation. Based on the above observations with other angiosperms also, can the scientist arrive at a law? If yes, explain the law. If not, give a justification for your answer. (Delhi 2016)

The scientist can come to two different laws, namely the law of dominance and the law of segregation, under the situation described in the topic (or the law of purity of gametes). 
This can be explained with the help of the following crosses:

In the F₁ hybrid two dissimilar alleles are present for one character, i.e., height T is for tallness and t is for dwarfness, out of which only one allele called the dominant allele expresses itself and the one which remains unexpressed is called the recessive allele. This is called the “law of dominance”.

The two dissimilar alleles that remain together in a heterozygous individual do not get mixed up and keep their distinct identity. Hence, at the time of gamete formation, they separate so that each gamete receives only one allele and is always pure which enables the reappearance of a recessive trait in F₂ progenies when the two recessive alleles come together. This is called the “law of purity of gametes.”