18 
ORGANOGRAPHY. 
BOOK I. 
its having tubercles on its surface. (Plate II. fig. 2.) Gene- 
rally, while cellular tissue is brittle, and has little or no cohe- 
sion, woody tissue has great tenacity and strength; whence its 
capability of being manufactured into linen. Every thing 
prepared from flax, hemp, and the like, is composed of woody 
tissue ; but cotton, which is cellular tissue, bears no comparison, 
as to strength, with either flax or hemp. 
Alphonse De Candolle gives the following as the result ob- 
tained by Labillardiere, as to the relative strength of diflerent 
organic fibres. He found that, in suspending weights to 
threads of the same diameter, 
Silk supported a weight equal to . . 34 
New Zealand flax, 2Sj 
Hemp, 16i 
Flax, Hi 
Pita flax (Agave Americana), ... 7 
That even the most delicate woody tissue consists of tubes, 
may be readily seen by examining it ^v-ith a high magnifying 
power, and also by the occasional detection of particles of 
greenish matter in its inside. (Plate II. fig. 2. b.) A very 
diflerent opinion has nevertheless been held by some physio- 
logists, who have thought that the woody tissue is capable of 
endless divisibility. " \Vlien," says Duhamel, " I have ex- 
amined under the microscope one of the principal fibres of a 
pear tree, it seemed to me to consist of a bundle of yet finer 
fibres; and when I have detached one of those fibres, and sub- 
mitted it to a more powerful magnifying power than the first, 
it has still appeared to be formed of a great number of yet 
more delicate fibres." (Physique des Arbres, i. 57.) To this 
opinion Du Petit Thouars assents, conceiving the tenuity of a 
fibre to be infinite, as well as its extensibility. (Essais sur la 
Vegetation^ p. 150.) These views have doubtless arisen from 
the use of very imperfect microscopes ; under low powers of 
which such appearances as Duhamel describes are visible; 
but with modern glasses, and after maceration in nitric acid, 
or even in pure water, each particular tube can be separated 
with the greatest facility. Their diameter is often very much 
less than that of the finest human hair ; the tubes of hemp, 
for example, when completely separated, are nearly six times 
