It doesnt really matter the tap root will always grow down, but if its facing up it may take longer to break ground, im guessing the biggest issue with people is the understanding of when u plant the seed at what stage. If u germinate in a paper towel then u would place the newely popped seed, root down, if ur planting the seed it might be better to do it root up. Either way if it grows it will break ground at some point due to the gravitational factors that influence root growth.