Introduction:
To determine the genotype of a tall pea plant with violet flowers, we can use a method called selfing. Selfing involves cross-pollinating the plant with itself, allowing us to observe the traits in the offspring and determine the genotype of the parent.

Procedure:
1. Select a tall pea plant with violet flowers as the parent plant for selfing.
2. Allow the plant to undergo self-pollination, either naturally or by manually transferring pollen from the anthers to the stigma of the same flower.
3. Once the self-pollination is complete, the plant will produce offspring.
4. Observe the traits of the offspring, specifically focusing on the two mentioned traits: plant height (tall or short) and flower color (violet or another color).
5. Record the phenotypes of the offspring in a Punnett square or similar diagram, taking into account the possible genotypes for each trait.
6. Analyze the phenotypic ratios of the offspring to determine the genotypes of the parent plant.

Genotypes and Phenotypes:
In pea plants, the tall trait (T) is dominant over the short trait (t), while the violet flower color trait (V) is dominant over other colors (v). The possible genotypes for the parent plant can be:

- TTvv: Homozygous dominant for plant height and homozygous recessive for flower color.
- TtVv: Heterozygous for both plant height and flower color.
- TTVV: Homozygous dominant for both plant height and flower color.

Observations:
1. If the parent plant is homozygous dominant (TTVV), all offspring will be tall with violet flowers (TtVv) since the dominant traits will be passed on.
2. If the parent plant is homozygous recessive (ttvv), all offspring will be short with other color flowers (ttvv) since only the recessive traits will be passed on.
3. If the parent plant is heterozygous (TtVv), the offspring will show a 3:1 phenotypic ratio. Approximately 75% of the offspring will be tall with violet flowers (TtVv), while 25% will be short with other color flowers (ttvv).

Determining the Genotype:
By observing the phenotypes of the offspring, we can determine the genotype of the parent plant. If the offspring show a 3:1 ratio of tall with violet flowers to short with other color flowers, it indicates that the parent plant is heterozygous (TtVv). If all the offspring have the same phenotype, it indicates that the parent plant is either homozygous dominant (TTVV) or homozygous recessive (ttvv).

Conclusion:
By selfing a tall pea plant with violet flowers and observing the phenotypes of the offspring, we can determine the genotype of the parent plant. The resulting ratios of the offspring will allow us to distinguish between homozygous dominant, homozygous recessive, and heterozygous genotypes for the two mentioned traits.