He was interested also in the subject of geotropism, and succeeded in proving that there is an innate tendency for the root to grow down and the stem to grow up; and that it is not merely a case of the root seeking the soil, and the stem the air. His directions for performing the experiment are as follows:--"Take a Box of _Moulds_, with a hole bored in the bottom, wide enough to admit the _Stalk_ of a _Plant_, and set it upon stilts half a yard or more above ground. Then lodg in the _Mould_ some _Plant_, for Example a _Bean_, in such sort, that the _Root_ of the _Bean_ standing in the _Moulds_ may poynt upwards, the _Stalk_ towards the ground. As the _Plant_ grows, it will follow, that at length the _Stalk_ will rise upward, and the _Root_ on the contrary, arch it self downward. Which evidently shews, That it is not sufficient, that the _Root_ hath _Earth_ to shoot into, or that its _Motion_ is only an _Appetite_ of being therein lodged, which way soever that be: but that its nature is, though within the _Earth_ already, yet to change its _Position_, and to _move Downwards_. And so likewise of the _Trunk_, that it rises, when a _Seed_ sprouts, out of the Ground, not meerly because it hath an _Appetite_ of being in the open _Aer_; for in this Experiment it is so already; yet now makes a new _Motion_ upwards." Although Grew cannot be called a great experimenter, he frequently took the easier course of throwing out suggestions for such work. "The generation of Experiments" he describes as "being like that of Discourse, where one thing introduceth an hundred more which otherwise would never have been thought of." Amongst other proposals he recommends that trial should be made of growing plants in common water, snow water, milk, oil, wine, ink, etc., or in any of these with solid bodies, such as nitre and salt, dissolved in them. He points out that the effect both on the plant and on the liquid should be noted. The solid body should be weighed before solution, and then, after the experiment is over, the liquid should be evaporated and the solid again weighed.