The Pear could penetrate Pores, that the other could not. Mr. _Evelyn_ says, in his Discourse of Forest-trees, ‘That a Pear will strike Root thro’ the roughest and most impenetrable Rocks and Clifts of Stone itself.’ He says likewise, in his _Pomona_, ‘That Pears will thrive where neither Apple or other Fruit could in Appearance be expected.’ I can scarce think, that a large Plant takes in larger Particles than a small one, for its Nourishment: If it did, I can’t believe, that the Thyme could have starv’d the Apricot-tree; it must have left the larger Particles of Food for that Tree, which probably would have sufficed to keep it alive: I rather think, that great and small Plants are sustain’d by the same minute Particles; for, as the fine Particles of Oats will nourish an Ox, so they will nourish a Tom-tit, or a Mite. Some Plants are of an hotter Constitution, and have a quicker Digestion, like Cormorants or Pigeons, devouring more greedily, and a greater Quantity of Food, than those of a colder Temperature, of equal Bulk, whose Sap, having a more languid Motion, in proportion to the less Degree of Heat in it, sends off fewer Recrements; and therefore a less Supply of Food is required in their room. This may make some Difference in the one’s succeeding the other; because the hot-constitution’d leaves not enough for its own Species to succeed again, but leaves enough for a Species of a colder Constitution to succeed it. But the Third and chiefest Cause of the Benefit of changing Sorts is Quantity of Tillage, in proportion to which the Food will be produced. The true Cause why Wheat is not (especially on any strong Soil) to be sown immediately after Wheat, is, That the first Wheat standing almost a Year on the Ground, by which it must grow harder; and Wheat Seed-time being soon after Harvest in _England_, there is not Space of Time to till the Land so much as a second Crop of Wheat requires. Tho’ sometimes in poorer Land, that is lighter, Wheat has succeeded Wheat with tolerable Success; when I have seen, on very rich strong Land, the first Crop lost by being much too big, and one following it immediately, quite lost by the Poorness of it, and not worth cutting. This was enough to satisfy, that the Tillage which was so much easier perform’d in less Time, sufficed for the light Land, but not for the strong: and, if the strong Land could have been brought into as good Tilth as the light (like as in the new Husbandry it may), it would have produced a much better second Crop than the light Land did. From all that has been said, these may be laid down as Maxims; _viz._ That the same Quantity of Tillage will produce the same Quantity of Food in the same Land[209]; and that the same Quantity of Food will maintain the same Quantity of Vegetables.