please do not ask me to rewrite all which is in the free pdf excerpt, which you obviously did not look into.
Es gibt übrigens auch einen Auszug auf deutsch, wenn Dir das lieber ist:
Let me start with telling about an incident instead.
I once was selling books at a seminar, when a guy came to me, looked at the title and solemny declared;
"There is no Zen in Aikido."
Sorry, but this man conveyed a very narrow-minded attitude.
Of course, as we know O-Sensei was in Omotokyo-Shintoism. But this does not at all eclude all other influences, like when you are Catholic you cannot be Protestant. That´s a very digital, western approach.
Therefore I would like to state, that although we may want to assume that during the development of Aikido no influnce of Zen was added, it had already been in the martial arts from which Aikido derived.