Vegetable Physiology, 81 



VEGETABLE PHYSIOLOGY. 



NUMBER THREE . 



The form of elementary tissue called Woody Fibre is so 

 named because it has been supposed to consist of fibres infi- 

 nitely divisible. It is now considered to be only a variety of 

 cellular tissue, in which the cells are much elongated, and lie 

 close to each other in bundles. It is possessed of great tenaci- 

 ty, and those plants in which it exists in the greatest perfection, 

 such as flax and hemp, are used in the manufacture of cordage. 

 If a fibre of hemp be examined by the microscope, it is found 

 to consist of a great number of smaller fibres adhering together, 

 and each of these is discovered to be a slender, transparent 

 tube, pointed at each end. Figure 5, a, represents a bundle 

 of this tissue, as it commonly exists. Its use in vegetable 

 economy appears to be, to convey fluids in the direction of its 

 length, and some observers have thought that each tube has a 

 pore at the end so as to afford a communication with the rest. 

 The especial oflice of this tissue in its adult state, is evidently, 

 to give strength and elasticity to those parts of the structure 

 which require support, and accordingly in all plants whose 

 stem is permanently elevated, as trees and shrubs, it is very 

 abundant. In these it receives additional consistence and 

 firmness from the deposition of various secretions within its 

 tubes, and a difference in the quantity or character of these 

 secretions produces the distinction between the inner portion, or 

 heart, of a tree, and the surrounding wood. In its hardest state 

 the tubes are entirely filled up, so that no sap can pass through 

 them. Figure 5, b, shows the appearance of woody fibre, 

 when the walls of its tubes are straight and parallel, and the 

 granules deposited by the permeating fluids begin to adhere to 

 them. Another variety of woody fibre is represented in Figure 

 5, c, and is called glandular woody fibre. This is peculiar to 

 the natural order Conifera, or cone bearing trees, such as the 

 Pine, Fir, and Juniper. It may be readily known by the 

 regular series of circular glandules, with an opaque centre, 

 which are found on the tubes of which it consists. They 



