Another instance in which he suggested an experiment, apparently without carrying it out, was in relation to the movements of the stems of non-climbing plants. He seems to have anticipated the nineteenth century discovery of nutation amongst plants other than climbers, though he stopped short of actually proving it. In his account of the Motions of Trunks he remarks, "The _Convolution_ of _Plants_, hath been observed only in those that Climb. But it seems probable, that many others do also _wind_; ... Whether it be so, or not the Experiment may easily be made by tying a _Thred_ upon any of the _Branches_; setting down the respect it then hath to any Quarter in the _Heavens_: for, if it shall appear in two or three Months, to have changed its Situation towards some other Quarter; it is certain proof hereof." He noticed that some plants twine "by _South_ from _East_ to _West_" and others "from _West_ to _East_," and attributed this to their being respectively under the influence of the sun and the moon. Whenever Grew's notions of plant physiology depended upon chemistry, they became, according to our modern ideas, extremely difficult to follow. He held, among many other curious beliefs, that salts obtained from any plant have a tendency to crystallise out in a form resembling that plant, and adds, as an illustration from the animal world, "though I have not seen it my self, yet I have been told by one that doth not use to phancy things, that the Volatile Salt of _Vipers_, will figure it self into the semblance of little _Vipers_." The mystical belief that characteristic "principles" permeate all things, finds expression in his idea that the "frost flowers," sometimes to be seen on a window pane, are evidence that the air is impregnated with "_Vegetable Principles_." Another fact, which he brings forward in support of the same view, is that the ground or water, when exposed for some time to air, turns green. His explanation, in this latter case, was not far from the truth, for, as we now know, the greenness is due to the vegetation of minute algæ, which, in their dormant state, may be carried from place to place by the wind. It is usual to regard Ecology as a very recent development of botanical science, but Nehemiah Grew seems to have been alive to the importance of the ecological standpoint,--though he did not describe it by this name. He writes "The proper _Places_ also of _Plants_, or such wherein they have ... a Spontaneous growth, should be considered. And that as to the _Climate_; whether in one Colder, Temperate, or more Hot. The _Region_; Continent, or Island. The _Seat_; as Sea, or Land, Watry, Boggy, or Dry; Hills, Plains, or Vallies; Open, in Woods, or under Hedges; against _Walls_, rooted in them, or on their Tops; and the like."