The first choice of emphasis available is the sower of the seed. Care must be given in placing importance on the sower for by grammatical construction the author has separated the sower from the parable. Separation of the sower from the main point of the story is further enhanced by his lack of action toward the growing of the seed. The sower sleeps and rises while the seed goes about the process of growing with no recorded input from the farmer. In all honesty the reader must admit to having never seen such a farmer before.
All farmers know how seeds grow and all farmers have input to enhance the growth of said seed.
With this in mind it is obvious that the farmer cannot be the true subject of this similitude. The second choice for subject of this parable could be the seed. In surrounding context we have the kingdom of God directly compared to a seed, but in this short similitude there is no such reference. However there is good evidence that the seed is an important part of this story and one that cannot be done without. As mentioned earlier the seed is cast with no concern for its destination.