This answer is from pitara.com/scienceforkids If you want to read the rest of the answer I suggest going to the site. It is pretty awesome! And too long to post here! Rosie

People have long wondered about this phenomenon until the answer was discovered and explained by the English naturalist Charles Darwin. He demonstrated that the growing shoot of a grass seedling always bends towards light. This is due to a phenomenon called phototropism.

I've noticed it too, Marina, but I'm not really the best judge because I live in the PNW and our weather is 8 months of straight rain, then 4 months of unending sun. By the time summer gets here my window plants are starved for it.

eeee science!!! I can't stress how cool I think plants are. :o) Much thank! I totally understand Tiffu... the weather has been awful here the past few years.

I was on mobile earlier, but I finally googled--here's the full answer if anyone else would like to see it. Also, here's a more science-y article that explains five major plant hormones which dictate their behavior (communication, growth, movement, etc).

Even more cool stuff that I haven't thought about in a while... Plants breathe cheerio-style! I actually found this over a year ago, but there's new studies that suggest plants have long term memory. A while back, I listened to an NPR interview with an ecology professor about whether or not trees can voluntarily care for/sense the presence of/talk to each other. They totally can--and it all came down to good ole fungi.

You think you know everything until you read about octopuses and plants! :o)

I wind up turning some plants daily as they start noticeably turning in a day, and on my west facing windows in particular. Will have to see if that changes in the winter though I'm sure it will!