ORGANIC COMPOUNDS OF PLANTS 177 



materials, are present largely as starch. The carbohy- 

 drates occur in plants in three physical forms : ( i ) As 

 the framework of the plant cells, as cellulose, (2) in 

 solution in the plant sap, as sugar, and (3) deposited as 

 solid substances within the plant cells like starch. In 

 coarse fodders, as hay, they are largely in the form of 

 cellulose and pentosan bodies. While the various carbo- 

 hydrates differ chemically and physically, they all possess 

 a few common characteristics : ( i ) they are all neutral 

 bodies, and (2) they all contain twice as many hydrogen 

 as oxygen atoms in their molecules. The H and O are 

 present in the same proportion as found in water, viz. , 

 2 atoms of H and i of O. In starch, C 6 H 10 O 5 , the H and 

 O would form 5H 2 O. 



Cellulose 



227. Occurrence. Cellulose is found most abundantly 

 in the stems, roots and leaves of plants, particularly at ma- 

 turity. Cellulose is the structural 



basis of the vegetable world, and 

 forms the framework of every 

 plant cell. In some plants it is 

 the most abundant material pres- 

 ent ; in hay and coarse fodders 

 it makes up from 30 to 40 per 

 cent, of the dry matter. Crops 

 like cotton, flax and hemp contain large amounts, and 

 are cultivated mainly for the cellulose which they yield. 



228. Physical Properties Pure cellulose is a colorless, 

 insoluble material, differing in texture according to its 



