24 
ORGANOGRAPHY. 
BOOK I. 
organic fibres. He found that, in suspending weights to 
threads of the same diameter, 
Silk supported a weight equal to . . 34 
New Zealand flax, 23f 
Hemp, 16^ 
Flax, 11| 
Pita flax (Agave Americana), ... 7 
That even the most delicate woody tissue consists of tubes, 
may be readily seen by examining it with a high magnifying 
power, and also by the occasional detection of particles of 
greenish matter in its inside. A very different opinion has 
nevertheless been held by some physiologists, who have 
thought that the woody tissue is capable of endless divisibility. 
When,” says Duhamel, “ I have examined under the mi- 
croscope 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 submitted 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 Arhres, i. 57.) To this opinion Du Petit 
Thouars assents, conceiving the tenuity of a fibre to be infi- 
nite, 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, each particular tube 
can be separated with the greatest facility. Their diameter 
is often very much less than that of the finest hunian hair; 
the tubes of hemp, for example, when completely separated, 
are nearly six times smaller. It must, however, be observed, 
that the fibres of this plant, as used in linen-making, are by 
no means in a state of final separation, each of the finest that 
meets the naked eye being in reality a bundle of tubes. 
While some do not exceed 30^00 of an inch in diameter, 
others have a diameter as considerable as that of ordinary 
cellular tissue itself; in Coniferse the tubes are often 
3 ^y, and in the Lime they average about yj-^. Link states 
(Elemental p. 85.) that they are very large in trees of hot 
