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Cardamine hirsuta
Small cluster of tiny, white 4-petaled blooms from a tall, erect stem. White flower centers. Erect seed pods come up from stem below the blooms. When seed pods are dry they explode open when disturbed (touched, brushed, etc) and send seeds flying. Cluster of low growing leaves at base of plant. Leaves divided into leaflets.
Suburban yard and garden. Seen growing in open, disturbed areas.
Mustard family. Edible as a bitter herb. Generally considered an invasive weed.
Glad I could help, even if I got the species wrong. I admit I ID'd it from a glance rather than keying it out. I'll try to do better with the other one. :)
I was doing a bit more research and I think this might actually be Hairy Bittercress, Cardamine hirsuta:
http://oregonstate.edu/dept/nursery-weed...
The way these plants grow is more consistent with that than the Pennsylvania Bittercress. While they are quite similar, my plant doesn't have branching blooms or leaves on the stem except for an occasional one (like image number 5). Your ID suggestion has helped though!
I have a special fondness for this one. Next time I get to my Newcomb's, I bet I'll have an ID on your other wildflower.