mer and autumn, when the young
suckers form on the wood; but my impression is that though all the several
substances are added annually, a little more pith going to the edges of the
pith-plates, and a little more bark to the bark, with a great deal more
wood to the wood,--there is a different or at least successive period for
each deposit, the carrying all these elements to their places involving a
fineness of basket work or web work in the vessels, which neither
microscope nor dissecting tool can disentangle. The result on the whole,
however, is practically that we have, outside the wood, always a mysterious
'cambium layer,' and then some distinctions in the bark itself, of which we
must take separate notice.

21. Of Cambium, Dr. Gray's 220th article gives the following account. "It
is not a distinct substance, but a layer of delicate new cells full of sap.
The inner portion of the cambium layer is, therefore, nascent wood, and the
outer nascent bark. As the cells of this layer multiply, the greater number
lengthen vertically into _prosenchyma_, or woody tissue, while some are
transformed into ducts" (wood vessels?) "and others remaining as
_parenchyma_, continue the medullary rays, or commence new ones." Nothing
is said here of the part of the cambium which becomes bark: but at page
128, the thin walled cells of the bark are said to be those of ordinary
'parenchyma,' and in the next page a very important passage occurs, which
must have a paragraph to itself. I close the present one with one more
protest against the entirely absurd terms 'par-enchyma,' for common
cellular tissue, 'pros-enchyma,' for cellular tissue with longer
cells;--'cambium' for an early state of _both_, and 'diachyma' for a
peculiar position of _one_![46] while the chemistry of all these substances
is wholly neglected, and we have no idea given us of any difference in
pith, wood, and bark, than that they are made of short or long--young or
old--cells!

22. But in Dr. Gray's 230th article comes this passage of real value.
(Italics mine--all.) "While the newer layers of the wood abound in _crude_
sap, which they convey to the leaves, those of the inner bark abound in
_elaborated_ sap, which _they receive from the leaves_, and convey to the
_cambium_ layer, or _zone of growth_. The proper juices and peculiar
products of plants are accordingly found in the foliage and bark,
especially the latter. In the bark, therefore, either of the stem or root,
med