128 TILLEES OF THE GBOUND CHAP. 



both for themselves and for their cattle, that it is 

 the grasses and peas and beans that feed humanity. 

 The leaves of many kinds of grasses, and of such 

 members of the Pea family as clover and lucerne, 

 form forage for the domestic animals, while the 

 seeds of other kinds feed man himself. 



Both families contain a considerable number of 

 annuals, that is of fast-growing plants Which throw 

 all their energy into seed -making, and die of 

 exhaustion as soon as their seeds are full-formed. 

 In consequence, the seeds are big and plump 

 and full of food material. Further, they are 

 for the most part without the poisonous sub- 

 stances found in many seeds, which render them 

 unfit for food ; they only require cooking to form 

 an important part of man's diet. 



Let us stop just for a moment at this word 

 " cooking," to ask ourselves why seeds cannot gener- 

 ally be eaten without cooking, while we often eat 

 fruits raw. The explanation is found easily if we go 

 back to the question of the contents of fruits and 

 seeds. We saw that fruits generally contain sugar, 

 while seeds generally contain much starch. Now 

 starch is difficult to digest when eaten raw ; it is 

 much easier to digest when it has been altered by 

 the heat used in cooking. We do not generally, it 

 is true, cook nuts, which are seeds full of starch ; 

 but then we eat very few nuts at a time. If we 



