And these are all the Pores the best Glasses, which, (when upon these Enquiries) we had at hand, would shew us. But the Learned and most Ingenious Naturalist Mr. Hook sheweth us moreover, besides these, a third, and yet smaller sort; the description whereof I find he hath given us amongst his Microscopical Observations. Of these Pores (as a confirmation of what, in [the Second Chapter], I have said of the Pores of the Lignous Body in general) he also demonstrates; that they are all continuous and prolonged by the length of the Trunk; as are the greater ones; the Experiment whereof he imparteth to be, by filling up, suppose in a piece of Char-coal, all the said Pores with Mercury; which appears to pass quite through them, in that by a very good Glass it is visible in their Orifices at both ends; and without a Glass, by the weight of the Coal alone, is also manifest.
Upon farther Enquiry, I likewise find, that the Pores of the Lignous Body in the Trunk of Plants, which at first only supposed, by the help of good Glasses are very fairly visible; each Fibre being perforated by 30, 50, 100, or hundreds of Pores. Or what I think is the truest notion of them, that each Fibre, though it seem to the bare eye to be but one, yet is indeed a great number of Fibres together; every Pore being not meerly a space betwixt the several pores of the Wood, but the Concave of a Fiber: So that if it be asked, what all that part of a Vegetable, either Plant or Tree, which is properly call’d the woody part; what all that is, I suppose, that is nothing else but a Cluster of innumerable and most extraordinary small Vessels or concave Fibres. [See Fig. 15.]
Next the Insertions of the Cortical Body, which in the Trunk of a Tree saw’d athwart, are plainly discerned as they run from the Circumference toward the Center; the whole Body of the Tree being visibly compounded of two distinct Substances, that of the several Rings, and that of the Insertions, running cross; shewing that in some resemblance in a Plain, which the Lines of Latitude and of the Meridian do in a Globe. [See Fig. 16.]
These Insertions are likewise very conspicuous in Sawing of Trees length-wayes into Boards, and those plain’d, and wrought into Leaves for Tables, Wainscot, Trenchers, and the like. In all which, as in course Trenchers made of Beech, and Tables of Oak, there are many parts which have a greater smoothness than the rest; and are so many inserted pieces of the Cortical Body; which by reason of those of the Lignous, seem to be discontinuous; although in the Trunk they are extended throughout its Breadth.
These Insertions, although as is said, of a quite distinct substance from the Lignous Body, and so no where truly incorporated with it, yet being they are in all parts, the one as the Warp, the other as the Woof, mutually braced and inter-woven together, they thus constitute one strong and firmly coherent Body.
As the Pores are greater or less, so are the Insertions also: To the bare eye usually the greater only are discernable: But through an indifferent Microscope there are others also, much more both numerous and small, distinctly apparent. So that, I think, we may observe, that as the grand Pith of the Trunk communicates with, and is augmented by the greater Insertions; so is the Pith of each greater Pore originated from the less; and those (at least) pithy parts in the Midling Pores, from others still less; and suppose, that the least of all are so far intruded into the smallest Pores, as only just to cause a kind of roughness on their concave sides, and no more; to what end shall be said. [See Fig. 17.]
In none of all these Pores can we observe any thing which may have the true nature and use of Valves, which is easily to admit that, to which they will by no means allow a regress. And their non-existence is enough evident, from what in [the first Chapter] we have said of the Lobes of the Seed: in whose Seminal Root, were there any Valves, it could not be, that by a contrary course of the Sap, they should ever grow; which yet, where-ever they turn into Dissimilar Leaves, they do. Or if we consider the growth of the Root, which oftentimes is upward and downward both at once.
The Insertions here in the Trunk give us likewise a sight of the position of their Pores. For in a plained piece of Oak, as in Wainscot, Tables, &c. besides the larger Pores of the Lignous Body, which run by the length of the Trunk; the Tract likewise of those of the Insertions may be observed to be made by the breadth, and so directly cross. Nor are they continuous as those of the Lignous Body, but very short, as those both of the Cortical Body and Pith, with which the Insertions, as to their substance are congenerous. Yet they all stand so together, as to be plainly ranked in even Lines or Rows throughout the breadth of the Trunk: As the Tract of these Pores appear to the naked Eye, [see in Fig. 18]. By the best Microscope I have at hand, I can only observe the Ranks of the Pores; not the Pores themselves, saving here and there one; wherefore I have not describ’d them.
The Pores of the Pith likewise being larger here in the Trunk, are better observable than in the Root: the width whereof, in comparison with their sides so exquisitely thin, may by an Honey-Comb be grosly exemplified; and is that also which the vast disproportion betwixt the Bulk and weight of a dry Pith doth enough declare. In the Trunks of some Plants, they are so ample and transparent, that in cutting both by the length and breadth of the Pith, some of them, even to the bare eye would seem to be considerably extended by the length of the said Pith; which once I also thought they were, and that only the rest of them were but short and discontinuous, and as ’tis said, somewhat answerable to the Cells of an Honey-Comb. This was the nearest we could come to them, by conjecture, and the assistance of the best Glasses we then had by us, when upon enquiry into the nature of the Pith: But that Worthy Person newly mentioned Mr. Hooke sheweth us, that the Pores of the Pith, particularly of Elder-Pith, so far as they are visible, are all alike discontinuous; and that the Pith is nothing else (to use his own words) but an heap of Bubbles.
Besides what this Observation informs us of here, it farther confirms what in [the second Chapter] we have said of the Original of the Pith and Cortical Body, and of the sameness of both their natures with the Parenchyma of the Seed. For, upon farther enquiry with better Glasses, I find, that the Parenchyma of the Plume and Radicle, and even of the Lobes themselves, though not so apparently, is nothing else but a Mass of Bubbles.