Perchloride of mercury applied to his lawn destroyed thousands of earthworms, but ruined the grass.

"The number of worms in your garden is astonishing … it will be an interesting observation, how soon the land is again stocked with worms, & whether the grass grows better before this happens. – I neglected to observe whether worms distruct [disturb?] the roots of grasses. – You will probably be able to borrow … my book On the Formation of Vegetable Mould … in which … you will find a good deal about the natural history of worms."