QI: bamboo and hello

I just watched QI (Stephen Fry on the ABC), I must have learned something... Bamboo can grow up to 4 meters a day - you can actually see it grow. I think I already knew that.

The word "Hello" was invented by Edison, he thought it was a nice clear sound when he used "Haloo" (hunting call) to make his first recording. Prior to that, "Hullo" was a sound of surprise, not greeting. Hullo, what's all this then? There was something about Hello being chosen as the word you say when answering the phone.