4 WHAT THE PLANT IS MADE OF [chap. 



Table I.— Composition of Meadow Grass from One Acre. 



So far we have only been dealing with the elements 

 common to all plants, which, as will be seen later, are 

 also common to animals as well ; but the elements are 

 only the raw material — bricks, stones, beams, mortar, 

 etc. — out of which all sorts of different edifices can be 

 constructed. There exist in fact in the plant material 

 certain characteristic groups of compounds, the members 

 of each group being built up in much the same way but 

 quite differently from the members of any other group, 

 although only the same elements may have been used 

 in the building of both groups. For example, the fats 

 form a definite class of bodies common in the seeds of 

 plants ; they are easily recognisable and are distinct in 

 every outward property from the sugars, another natural 

 group of substances found in plants. Yet both fats and 

 sugars contain the same elements — carbon, hydrogen, 



