From the “100 Years Ago” feature in today’s Nature:

It may interest some to know that radium destroys vegetable matter. I happened to replace the usual mica plates, used to keep in the small quantity of radium in its ebonite box, with a piece of cambric, so as to permit the whole of the emanations to pass out, mica stopping the gamma rays. In four days the cambric was rotted away. I have replaced it now several times with the same result.

Hmmm. A clue.