26 VEGETABLE ELEMENTS AND TISSUES. 



or pleurenchyma (jr\evpa, rib, e^vfjua), from its 

 strength. 



The walls of the cells of woody tissue are often 

 covered with dots, either simple or with an inner dot 

 (PL I. fig. 6 b, fig. 11 b), or with streaks (PL I. fig. 6 a) 

 or with a spirai fibre (fig. 11 b, c), either alone or 

 with dots also. 



This tissue is of great importance in plants, from 

 its strength and flexibility; it forms a considerable 

 part of the veins of leaves, the inner bark (liber), and 

 of the wood of the stems of trees. It is also very useful 

 to man : for it constitutes hemp, of which rope and 

 string are made ; flax, of which linen is made ; cocoa- 

 nut fibre ; bast, used by gardeners for tying up plants, 

 which is the inner bark of the lime ; and jute, which 

 is the inner bark of an Indian lime-tree. 



In the white woody part of the stems of trees be- 

 longing to the fir-order (Conif erse), as a piece of deal 

 or pine, which is mainly composed of wood- (prosen- 

 chymatous) cells, the cells exhibit rows of minute 

 circular markings (PL I. fig. 10). These were for- 

 merly supposed to be solid bodies or glands ; hence the 

 tissue is still sometimes called glandular. Within the 

 outer ring of each marking is an inner central dot, or 

 sometimes an oblique streak. The side view of the 

 cells (PL I. fig. 8 a), which is seen in a tangential 

 section, shows that the markings are minute pits, 

 each being opposite to one of an adjacent cell, and 

 sunk inwards towards the centre of the cell, the inner 

 dot or streak being a thinner portion of the cell-wall. 

 This glandular tissue of the Coniferse is interesting as 

 forming a test-object for the defining power of the 

 microscope, which should show the two rings sharply 

 and free from colour ; the section of the wood should 

 be examined as a dry transparent object. 



The difference between the woody fibre and the wood- 

 cells of coniferous wood may also be seen well in a piece 

 of deal, as cut up for fire-wood. If the end of a stick of 



