The correct answer is option 2 - seed coat impermeability. This means that the outer covering of the seed is unable to absorb water, which is necessary for germination. In some plants, the seed coat may be too thick or hard, preventing water from entering the seed and initiating the germination process. However, when the seeds pass through the digestive tract of fruit-eating birds, the acids and enzymes in the bird`s digestive system can soften or break down the seed coat. This allows water to penetrate the seed and triggers germination. It is important for these plants that their seeds pass through the digestive system of birds in order to have a chance to grow into new plants. Therefore, seed coat impermeability is the reason why the seeds fail to germinate if they do not go through the digestive tract of fruit-eating birds.