[6] This is meant of dry Earth, by its Lightness (when pulveriz’d extremely fine) carried in the Air without Vapour: For the Atmosphere, consisting of all the Elements, has Earth in it in considerable Quantity, mix’d with Water; but a very little Earth is so minutely divided, as to fly therein pure from Water, which is its Vehicle there for the most Part. They might as well believe, that _Martins_ and _Swallows_ are nourish’d by the Air, because they live on Flies and Gnats, which they catch therein; this being the same Food, which is found in the Stomach of the Chameleon. If, as they say, the Earth is of little other Use to Plants, but to keep them fix’d and steady, there would be little or no Difference in the Value of rich and poor Land, dung’d or undung’d; for one would serve to keep Plants fix’d and steady, very near, if not quite as well as the other. If Water or Air was the Food of Plants, I cannot see what Necessity there should be of Dung or Tillage. 4. _Fire_. No Plant can live without Heat, tho’ different Degrees of it be necessary to different Sorts of Plants. Some are almost able to keep Company with the _Salamander_, and do live in the hottest Exposures of the hot Countries. Others have their Abode with Fishes under Water, in cold Climates: for the Sun has his Influence, tho’ weaker, upon the Earth cover’d with Water, at a considerable Depth; which appears by the Effect the Vicissitudes of Winter and Summer have upon subterraqueous Vegetables. Tho’ every Heat is said to be a different Degree of Fire; yet we may distinguish the Degrees by their different Effects. Heat warms; but Fire burns: The first helps to cherish, the latter destroys Plants. 5. _Earth_. That which nourishes and augments a Plant is the true Food of it. Every Plant is Earth, and the Growth and true Increase of a Plant is the Addition of more Earth. _Nitre_ (or other Salts) prepares the Earth, Water and Air move it, by conveying and fermenting it in the Juices; and this Motion is called Heat. When this additional Earth is assimilated to the Plant, it becomes an absolute Part of it. Suppose Water, Air, and Heat, could be taken away, would it not remain to be a Plant, tho’ a dead one? But suppose the Earth of it taken away, what would then become of the Plant? Mr. _Bradley_ might look long enough after it, before he found it in the Air among his specific or certain Qualities. Besides, too much _Nitre_ (or other Salts) corrodes a Plant; too much Water drowns it; too much Air dries the Roots of it; too much Heat (or Fire) burns it; but too much Earth a Plant never can have, unless it be therein wholly buried; and in that Case it would be equally misapply’d to the Body, as Air or Nitre would be to the Roots. Too much Earth, or too fine, can never possibly be given to Roots; for they never receive so much of it as to surfeit the Plants, unless it be depriv’d of Leaves, which, as Lungs, should purify it.