Answer: sunlight
Step-by-step explanation:
The condition that is probably very important for the germination of these types of seeds is sunlight.
Since she noticed that some seeds germinated and some did not. She noticed that the seeds that had thick layers of branches and leaves overhead did not germinate. This was because the seed covered didn't receive sunlight.
Without the sun, we should note that plants would not be able to grow, and survive. Apart from water, and carbon dioxide, sunlight is also important for the growth of plant.
Through photosynthesis, the energy gotten by the plants from the sun will be converted to the nutrients needed to make food.