I am teaching biology in an academy. The question which I had asked above had been raised by on of my students. I tried my level best to search out the answer to this question but I could not find the answer. I had read a number of answers to different questions from this website. So that's why I thought to Post my question on your website
I like the reference book Plant Physiological Ecology for stuff like this. I know one of the authors is Thijs Pons.
When temperatures become high, plants may close the stomata to conserve moisture. When the stomata are open, usually in daylight hours, the open stomata allow $CO_2$ to enter the leaf. This carbon is needed to form glucose and many other products a plant makes from photosynthesis. Most plants will not open the stomata in the absence of light.
(I use the above text as the reference. I can't give you pages right now, but I was reading this a couple of days ago.)