One true use of the _Pith_ is for the better Advancement of the _Sap_, whereof we shall speak in the next Chapter. The use we here observe is for the quicker and higher Fermentation of the _Sap_: For although the Fermentation made in the _Cortical Body_ was well subservient to the first Vegetations, yet those more perfect ones in the _Trunk_ which after follow, require a Body more adapted to it, and that is the _Pith_; which is so necessary, as not to be only common to, but considerably large in the _Roots_ of most Plants; if not in their inferiour parts, yet at their tops. Where though either deriv’d or amplify’d from the _Cortical Body_, yet being by its Insertions only, we may therefore suppose, as those, so this, to be more finely constituted. And being also from its co-arctation, while inserted, now free; all its Pores, upon the supply of the _Sap_, will more or less be amplified: Upon which accounts, the _Sap_ thereinto received, will be more pure, and its fermentation therein more active. And as the _Pith_ is superiour to the _Cortical Body_ by its Constitution, so by its Place. For as it thus stands central, it hath the _Lignous Body_ surrounding it. Now as the Skin is the Fence of the _Cortical Body_, and that of the _Lignous_; so is the _Lignous_ again a far more preheminent one unto the _Pith_; the _Sap_ being here a brisk Liquor, tunn’d up as in a wooden Cask. And as the _Pith_ subserves the higher Fermentation of the _Sap_; so do the Insertions its purer Distribution; that separation which the parts of the _Sap_, by being fermented in the _Pith_, were dispos’d for; being, upon its entrance into the Insertions, now made: So that as the Skin is a Filtre to the _Cortical Body_, so are the Insertions a more preheminent one to the _Lignous_; and as they subserve the purer, so the freer and sufficient distribution of the _Sap_: For the _Root_ enlarging, and so the _Lignous Body_ growing thicker, although the _Cortical_ and the _Pith_ might supply _Sap_ sufficient to the nutrition of its Parts next adjacent to them; yet those more inward, must needs be scanted of their _Aliment_; and so, if not quite starv’d, yet be uncapable of equal growth: Whereas the _Lignous Body_ being through its whole breadth frequently disparted, and the _Cortical Body_ inserted through it; the _Sap_ by those Insertions, as the Blood by the disseminations of the _Arteries_, is freely and sufficiently convey’d to its intimate Parts, even those which from either the _cortical Body_ or the _Pith_ are most remote. Lastly, as the consequent hereof, they are thus assistant to the Latitudinal growth of the _Root_; as the _Lignous Body_ to its growth in length; so these Insertions of the _Cortical_, to its better growth in breadth.