The first thing that comes to mind is the bolting of those delicious lettuces that grow in the early season. Once the sun of summer starts hitting those delicate lettuces they are either wilted in the heat or they rush to seed. Of course there are also those knock down, drag out summer days that can even threaten the most sun loving plants out there. I have seen tomatoes get a little shy in the unreasonable heat of mid summer.
This article touches on the fact of managing shade and sun. When it comes to gardening the options are very important. In a way gardening is very much a microcosm of survival. You must be prepared to adapt in the event of things like this. The author will give you some great signs to tell whether the sun is beating your plants down.