DIGESTION OF RESERVE-MATERIALS 231 



emulsin, and gives rise to benzoic aldehyde, prussic acid and 

 glucose according to the following equation : — 



C20H27NO11 + 2H2O = CyHgO + HCN + aCgHjaOg 



Amygdalin Benzoic prussic glucose 



aldehyde acid 



The glucoside sinigrin is decomposed by the enzyme myrosin 

 as explained on page 370. 



(v) A large amount of reserve-material in the seeds of flax, 

 colza, castor-oil and other plants exists in the form of oil or fat. 

 During the germination of such seeds the oil suffers hydrolysis 

 through the activity of an enzyme which has been named lipase. 

 The products of the decomposition in those cases which have 

 been carefully examined appear to be free fatty acids and 

 glycerin : the fate of the former substances is not clear, but it 

 is probable that the glycerin is transformed into some kind of 

 sugar which travels into the tissues of the growing embryo where 

 some of it is not unfrequently converted into a temporary 

 reserve of small starch-grains. 



(vi) Another group of enzymes exists in plants by means of 

 which the various insoluble and indiffusible proteins are hydro- 

 lysed into simpler diffusible proteins, termed peptones, together 

 with a larger or smaller amount of amides. So far as they have 

 been examined they all resemble the enzyme secreted by the 

 pancreas of the higher animals, and are termed vegetable trypsins. 



The chemical changes which proteins undergo in their migra- 

 tion from place to place within the tissues of plants are not the 

 same in all cases, but the reserve proteins of many seeds are 

 made available for the embryo through the action of tryptic 

 ferments. When germination begins the insoluble and slowly 

 diffusible proteins in the cotyledons and endosperm are decom- 

 posed into soluble peptones, and one or more amides, such as 

 asparagine, leucine or tyrosine, all of which substances circulate 

 readily to the various parts of the growing embryo needing 

 nitrogenous nutriment. 



