350 FRUITS AND SEEDS 



c. Digestion in Seeds ; Enzymes. It is in connection 

 with the germination of seeds that digestion in plants may 

 be best considered. You know that digestion is just as 

 universal a process among plants as it is among animals ; 

 food must be transformed from solid to liquid before it 

 can be used in the cells of either plants or animals (see 

 page 42). 



To understand digestion it is necessary to know some- 

 thing about enzymes, and of these you may have heard in 

 your study of the human body. Enzymes are present in 

 the saliva, in the gastric juice, and in the intestines. They 

 are substances that cause other substances to change; 

 they are the agents of digestion, which cannot occur without 

 them ; they change insoluble substances to soluble ones, 

 and they may change insoluble ones back into solution 

 again. It is an enzyme, for example, which causes starch 

 to change to sugar, and the same enzyme may reverse its 

 action and change sugar back again to starch. 



With all the changes of substances from solid to liquid 

 and back again which are constantly going on in plant 

 life, it is evident that enzymes have a very important part 

 to play. Enzymes are manufactured by the protoplasm. 



One of the properties of enzymes is that in causing 

 other substances to change they do not, apparently, change 

 themselves. This being the case, a very small amount 

 of an enzyme is able to cause changes in very considerable 

 amounts of other substances. Many enzymes, so small 

 in amount that they could not be separated out from the 

 tissues in which they work, were recognized first by the 

 changes which they caused. Though they themselves may 

 not be evident, the work which they do is very evident. 

 Thus, in the case of the coconut, during germination 



