42 



HOW CROPS 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 

 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, a], hemp, 

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

 unsized paper made from these materials, 

 are nearly pure cellulose. 



The fibers of cotton, hemp, and flax are simply 

 long and thick-walled cells, the appearance of 

 which, when highly magnified, is shown in Fig. 11, 

 where a represents the thinner, more soft, and col- 

 lapsed cotton fiber, and b 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 fill up interiorly by the deposition of re- 

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

 grown with other substances.* The bard 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 

 "lignin." On this view, according to F. Schulze, ligniu Impregnates 

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

 and is readily oxidi/cd by nitric acid. Schulze ascribes to it the com- 

 position 



Carbon 55.3 



Hydrogen 5.8 



Oxygen 38.9 



100.0 



This is, however, simply the inferred composition of what is left after 

 the cellulose, !(.. lia\ e'been removed. "L,igniii " cannot be separated 

 in the pun- state, and has never been analy/.ed. What is thns desig- 

 nated is a mixture of se\-era 1 i list met substances. Kremy's lignose. \\ii- 

 none, lignin, and lignireose. as well as .1. Krdman's glycollgnose and 

 lignose, are not established as chemically distinct substances. 



Fig. 11. 



