Hi,

The main question is what do you want to extract exactly. Are you planing to do a general metabolite analysis or looking for a specific class of substances. Roots and leaves can be extracted with various alcohols or even buffers but again it depends on the purpose. The bark will contain cellulose, lignin and a bunch of other molecules that are difficult to dissolve if that is the purpose. You might need acids and/or heating. You have to be more precise regarding the purpose of the extraction and then you would get better advice.

Good luck!