Hi Rick .......
>>>>> A rose can be well watered, but if the transpiration rate is higher than the plant can pull moisture up to the top growth,
I think you're completely right. Plus, plain old tissue temperatures might prevent blooms - I've read that tomatoes stop blooming or setting fruit around (??) 90 or 95 F (??).
Yes, you are right about tissue structure in a rose can impact its heat tolerance. I have found that roses with thick petal substance and dense foliage are the most successful roses in my heat zone. That leaves out a lot of different classes of roses, but fried blooms are not all that attractive.
I am certain that must be true for a lot of other types of plants.
I know from experience that the fruit set of tomatoes is impacted by high temps. If my toms have not blossomed before the heat hits, I end up with a low yield for the season.
I do get a lot of general information from the UCDavis site and know several of the people in their horticultural department ... funny how we all end up meeting people through our gardening hobby ... that have been quite helpful. The problem comes down to finding the right cultivars that will do well at a higher elevation with more intense light and high heat.
My night temps can swing down as much as 50 degrees which gives me an advantage in that the plants have time to rehydrate, while UC Davis is located down in the valley where the night temps don't cool off, so we are always guessing about what will work.
Thanks for the links. I'll check them out tonight. I am off to go collect mulch before it rains. 
Smiles,
Lyn
