Ask HN: Where can I find studies that link office plants to productivity

As part of a cost cutting measure at my workplace we've just had all the office greenery removed. In it's place we've got nothing but drab grey walls to look at.

If anyone knows of any papers that have been written that link office greenery to increased productivity could you post them in the comments. This way I might have an argument to take to the Higher-Ups about getting the greenery reinstated. Thanks