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 thino- 

 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 different 

 organic fibres. He found that, in suspending weio-hts to 

 threads of the same diameter, 



Silk supported a weight equal to . . 34 



New Zealand flax, 23a 



Hemp, 161 



Flax, 113. 



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. (Plate II. fig. 2. b.) A very 

 different opinion has nevertheless been held by some physio- 

 logists, who have thought that the woody tissue is capable of 

 endless divisibility. " When," 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 Arhres, 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 douljtless 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. Tlieir 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 



