Does planting a sapling on farmland help it grow?

From BlockSapling.java:

public void growTree(World world, int i, int j, int k, Random random)
    {
        int l = world.getBlockMetadata(i, j, k) & 3;
        world.setBlock(i, j, k, 0);
        Object obj = null;
        if(l == 1)
        {
            obj = new WorldGenTaiga2();
        } else
        if(l == 2)
        {
            obj = new WorldGenForest();
        } else
        {
            obj = new WorldGenTrees();
            if(random.nextInt(10) == 0)
            {
                obj = new WorldGenBigTree();
            }
        }
        if(!((WorldGenerator) (obj)).generate(world, random, i, j, k))
        {
            world.setBlockAndMetadata(i, j, k, blockID, l);
        }
    }

There is no reference to the block the sapling is planted on.

(While world.getBlockMetaData(i, j, k) looks suspicious, it is simply looking up what kind of tree the sapling should grow — pine, birch, or "normal".)