|MadSci Network: Botany|
An excellent question, Zenash!
First off, let me tell you a little bit about the process we call germination. There are three phases. The first phase involves the seed taking up water. During this time, the seed increases in size. In the second phase, the plant begins to digest the food stored in the seed. The final phase is when the root starts to grow down and the stem reaches for the surface. After the stem emerges from the soil, the frist true leaves will expand and the photosynthisis will start. The term "germination" refers to the expansion of the root and shoot from the seed, not the emergence of the plant from the soil.
The depth of a seed will very much effect the growth of a plant. Until a plant emerges, it has to rely on the stored food in the seed. The deeper the seed, the more stored food it takes to reach the surface. Needless to say, small seeds do not have a lot of stored food and may never reach the surface if planted too deep.
There are a lot of factors that will effect the germination of a seed. Some seeds have to have something happen to them before they will grow. This is called a dormancy requirement. Depending on the plant species, the seed may require cold periods (stratification), soaking, or cracking the seed coat (scarification). These requirements can be met in nature by overwintering on the ground, being submerged by a spring rain, or being swollowed by an animal, respectivly. This dormancy is a way to keep new plants from growing right next to the parent plant or keep them from growing in the fall only to be quickly killed by the winter frost.
Once the dormancy is broken, temperature and moisture are the most important aspects to weither a seed will germinate. In addition, some seeds are photosensitive, meaning they have to have light or darkness to grow.
To sum it up, germination of the seeds is not necessarly related to planting depth. What you would actually be measuring is the plant's ability to emerge from that depth. An interesting addition to your experiment might be to wrap a few seeds in a wet papertowel and see how many germinate. All seeds sold should have a germination percentage on the package. The papertowel test is a good way to check this number.
A brief article on Wildflower Germination
A link containing a lot of information on how to germinate different perennials
Eric J. Biddinger
Purdue Cooperative Extension
Try the links in the MadSci Library for more information on Botany.