Mr. ellis on the Gorgonia. 
white diaphragms , feparated from one another about the 
diftance of their own diameter. But thefe crofs mem- 
branes are found to be more numerous in fuch as have 
been preferred di redly from the fea in fpirits ; and when 
they are examined in the microfcope, they appear to be 
of the nature and fubftance with the lamina that com- 
pofe the horny tube that furround thennw. 
(c) While I was comparing the longitudinal fedlions of the young branche 
of trees with thofe of the gorgonia , I was furprized to find fuch a fimilitude be- 
tween the pith of a branch of a walnut tree, of a year’s growth, and that of the 
gorgonia , fee grew, / }nat . of Plants , tab. xix. fig. 4. A. and B.; efpecially as we 
are told by a modern author, who hath publifhed many microfcopical obfervations 
on the conftrudlion of timber, that the cell-like divifions in the branch of a wal- 
nut tree are only a row of fingle blebs of pith. But the microfcope difcovers to 
us, on viewing one of thefe crols membranes, that it is compofed of many cells 
fhrunk up and united together; for, upon viewing the flat furface of one of them, 
it appeared full of circles interfering one another, like a thick tranfverfe fe£fion 
of many other dried piths preffed together: befides, the thicker part of this 
fhrunk-up walnut pith, all round next the infide clofe to the wood, when mag- 
nified, plainly fhewed the fame appearance of blebs as in other pith. To con- 
firm this obfervation, May 23, 1772, I procured a young green fhoot of a wal- 
nut tree, growing from a branch of the preceding year; and examining the pith, 
both in upright and tranfverfe fe&ions of this new fhoot, I found that they exadfly 
refembled the pith of many other trees, but were full of fap: and that the ranges 
of cells or blebs that occupied one of thefe fpaces could not be lefs than a hun- 
dred, perhaps double that number of blebs. Dr. grew takes notice, p. 120. in 
his Anatomy of Plants , that there are other trees befide the walnut tree whofe pith 
in the laft year’s fhoot fhrinks up and forms fuch cavities; and an ingenious 
friend of mine, now engaged in an enquiry into the ftru&ure of plants, hath 
fhewn me a laft year’s ftem of the brajftca fylvejlris , or fhrubby cabbage, whofe 
pith is fhrunk and divided into a fingle row of cells, like thofe of the walnut tree 
of laft year’s growth. 
I come 
