can anyone identify these bumps on tree leaves?

my neighbour and i just noticed these ugly bumps all over the leaves of her alder tree i think she said, don't quote me, they are green on the top side and a rusty yellow/brown on the bottom....what are they, and how do we get rid of them? thank you! i tell her you people are just amazing....trying to get her to join as she loves gardening....thanks again!

 

Appear to be Populus leaves, look up problems of those trees.

 

unfortunately we checked the online info about poplar trees and found not a single one that matches...these bumps are on a good 60% of all the leaves but the tree looks healthy otherwise. there is no noticeable bug activity on tree or under it.

 

Next time use this site. I found what appears to be the appropriate page in seconds.

http://pnwhandbooks.org/plantdisease/poplar-populus-sp-leaf-blister

 

Edema, maybe?

 

thanks again. definitely leaf blister. we had looked together through 3 pages of google 'suggested sights' for our question...nothing matched. i told my girlfriend its time to find a better search engine!