Here are two things that I have not see anywhere else in my research on the subject.
First, I will explain why coconut trees at the edge of the beach seem to "reach" toward the sea, but usually go straight up when planted away from the beach. Then I will get to why the coconut tree puts a liquid in its seed.
The main purpose of many seeds is to to take themselves away from the parent to start a new life somewhere else (hopefully better). Just like us humans the coconut tree wants it's offspring to migrate. It uses the sea as the medium on which it travels. The coconut is too heavy to move toward the sea using wind or animals. It's also too tough for most animals to be able to get the nutrition locked inside it. So the tree, which in nature would most likely find itself on a beach, contorts itself so that it's "head" is above the sea and then it drops is seed in the ocean to travel and find a new place to grow and propagate. That would be my reasoning for explaining the commonly seen phenomenon of coconut trees leaning over the ocean.
So now that the coconut has started it's travels into the unknown, it needs to find a place to grow. The seed bobs up and down on the ocean until it lands somewhere. It could land on the same island or travel thousands of kilometers and land on another island or coral atoll or a sandbar. This is where the liquid comes in to play. The liquid which has been moving inside the coconut suddenly stops. After a certain amount of time the next step in it's growth is triggered because of the still liquid. Also, the cavity in the coconut keeps it from drowning.
That's it. The "water" is a "level" that tells the coconut when to "drop a root and send a shoot"
Let me know what you think.