NUTRIENTS. 35 



they are composed simply of carbon, and the elements of 

 water hydrogen and oxygen. 



Cellulose. The cellular structure of all plants, and of 

 the trunks of trees, consist of this substance. It consti- 

 tutes the frame-work of plants; and the cells of this 

 frame-work are internally coated, or incrusted with a harder 

 and tougher substance, called lignin. These two substan- 

 ces are so much found together, and their chemical com- 

 position is so nearly alike, that they may properly be 

 considered together. 



Pure cellulose has the same chemical composition as 

 starch, and all woody fibres can be changed into starch by 

 heat and by acids. 



The dried stalks of all grass and fodder plants are com- 

 posed largely of cellulose. 



EFFECT OF HEAT UPON WOODY FIBRE. J. P. W. John- 

 ston quotes from Schiibler the following : " If wood be 

 reduced. to the state of fine sawdust, and be then boiled in 

 water to separate everything soluble, afterwards dried by a 

 gentle heat, then heated several times in a baker's oven, it 

 will become hard and crisp, and may be ground in tEe mill 

 into fine meal. The powder thus obtained is slightly yel- 

 low in color, but has a taste and smell similar to the flour 

 of wheat ; it ferments when made into paste with yeast or 

 leaven, and when baked gives a light, homogeneous bread. 

 Boiled with water, it yields a stiff, tremulous jelly like that 

 from starch." 



It thus appears, that by the agency of heat, woody fibre 

 may be changed into starch. 



EFFECT OF ACID UPON IT. If these parts of fine saw- 

 dust, or fragments of old linen be rubbed in a mortar with 

 four parts of sulphuric acid, added by degrees, it will, in 

 15 minutes, be rendered completely soluble in water. If 

 the solution in water be freed from acid with chalk, and 



