42 



HOW CKOPS GROW. 



Nearly all plants and all their parts contain cellulose, 



but it is relatively most abundant in 



' stems and leaves. In seeds it forms a 



WM III large portion of the husk, shell, or other 



outer coating, but in the interior of the 



seed it exists in small proportion. 



The fibers of cotton (Fig. 11, d), hemp, 

 and flax (Fig. 11, V), and white cloth and 

 r« \lt1) unsized paper made from these materials, 

 J[f are nearly pure cellulose. 



The fibers of cotton, hemp, and flax are simply 

 ni« long and thlck-waUed cells, the appearance of 



|Mk \ \^k wliich, when highly magnified, is shown in Fig. 11, 

 \Sil li^^^ where a represents the thinner, more soft, and col- 

 IKI \^K lapsed cotton fiber, and 6 the thicker and more dur- 

 able fiber of linen. 



Wood, or woody fiber, consists of long 

 and slender cells of various forms and di- 

 mensions (see p. 293), which are delicate 

 when young (in the sap wood), but as 

 they become older fiU up interiorly by the deposition of re- 

 peated layers of cellulose, which is more or less inter- 

 grown with other substances.* The hard shells of nuts 

 and stone fruits contain a basis of cellulose, which is im- 

 pregnated with other matters. - 



When quite pure, cellulose is a white, often silky or 

 spongy, and translucent body, its appearance varying 



* Wood was formerly supposed to consist of cellulose and so-called 

 "llgnln." On this view, according to F. Sohulze, llgnin impregnates 

 (not simply incrusts) the cell-wall, is soluble in hot alkaline solutions, 

 and is readily oxidized by nitric acid. Schulze ascribes to it the com- 

 position 



Carbon 65.3 



Hydrogen 5.8 



Oxygen 38.9 



100.0 



Tills is, however, simply the Inferred composition of what is left after 

 the cellulose, etc., have been removed. *' Llgnln " cannot be separated 

 in the pure state, and has never been analyzed. What is thus desig- 

 nated is a mixture of several distinct substances. Fremy 's lignose, Ug- 

 none, llgnln, and llgnireose, as well as J. Erdman's glycolignose and 

 lignose, are not established as chemlcaUy distinct substances. 



