Answer: Your elm tree is showing stress from a wound and the dark, wet area is a puddle of sap that has run out of the injury. Insects, animals and even garden equipment can damage the trunks of trees. Wounds such as these usually heal on their own.
The wrinkled leaves on your plum tree indicate insect damage while the leaves are still unopened. Insect feeding will cause them to look crinkled when they fully open. You'll want to check your tree very early in spring just as the leaf buds are forming. Look for insects such as aphids or beetles. If you find them, an insecticide will take care of them and next year the leaves should unfurl without damage.
Good luck with your garden!
Q&A Library Searching Tips