But it must be noted, that the Depth of the Glass protected the Roots therein from the Injury of the Motion of the free Air, which would have dry’d them, if they had been out of the Glass. In this Trough is shewn most of the Hoing Effects; _viz._ That Roots, by being broken off near the Ends, increase their Number, and send out several where one is broken off. That the Roots increase their Fibres every time the Earth is stirr’d about them. That the stirring the Earth makes the Plants grow the faster. LEAVES are the Parts or Bowels of a Plant, which perform the same Office to Sap, as the Lungs of an Animal do to Blood; that is, they purify or cleanse it of the Recrements, or fuliginous Steams, received in the Circulation, being the unfit Parts of the Food; and perhaps some decay’d Particles, which fly off the Vessels, through which Blood and Sap do pass respectively. Besides which Use, the Nitro-aerous Particles may there enter, to keep up the vital Ferment or Flame. Mr. _Papin_ shews, that Air will pass in at the Leaves, and out thro’ the Plant at the Roots, but Water will not pass in at the Leaves; and that if the Leaves have no Air, a Plant will die; but if the Leaves have Air, tho’ the Root remain in Water _in vacuo_, the Plant will live and grow. Dr. _Grew_, in his Anatomy of Plants, mentions Vessels, which he calls, Net-work, Cobweb, Skeins of Silk, _&c._ but above all, the Multitude of Air-Bladders in them, which I take to be of the same Use in Leaves, as the Vesiculæ are in Lungs. Leaves being as Lungs inverted, and of a broad and thin Form; their Vesiculæ are in Contact with the free open Air, and therefore have no need of Trachea, or Bronchia, nor of Respiration. CHAP. II. _Of_ FOOD _of_ PLANTS. The chief Art of an Husbandman is to feed Plants to the best Advantage; but how shall he do that, unless he knows what is their Food? By Food is meant that Matter, which, being added and united to the first _Stamina_ of Plants, or _Plantulæ_, which were made in little at the Creation, gives them, or rather is their Increase. ’Tis agreed, that all the following Materials contribute, in some manner, to the Increase of Plants; but ’tis disputed which of them is that very Increase or Food. 1. _Nitre_. 2. _Water_. 3. _Air_. 4. _Fire_. 5. _Earth_. I will not mention, as a Food, that acid Spirit of the Air, so much talk’d of; since by its eating asunder Iron Bars it appears too much of the Nature of _Aqua Fortis_, to be a welcome Guest alone to the tender Vessels of the Roots of Plants.