CHANGES IN THE STORED FOOD 93 



Germinative Processes 



Seeds need water, oxygen, and warmth in germination because 

 upon these external factors the internal germinative processes 

 depend. For dissolving and transporting foods water is indis- 

 pensable; the occurrence of certain chemical processes depends 

 upon oxygen; and in order for both chemical and physical proc- 

 esses to be suitably active, as previously shown (page 90), 

 warmth is required. 



Changes in the Stored Food. — The first of the germinative 

 processes has to do with the digestion and translocation of the 

 stored foods. Whether stored outside of the embryo or in the 

 cotyledons, the stored foods, until brought nearer, are beyond 

 the absorptive reach of the cells of the plumule and radicle where 

 they are most needed. But unless foods are in solution, which is 

 the only form in which they can pass through the walls and proto- 

 plasm of cells, they can not move from one region of a plant to 

 another. Therefore, since starch, fat, and protein, which are the 

 chief storage foods of seeds, are not readily soluble in water, they 

 must be changed to sugar, fatty acids, peptones, or other soluble 

 forms before being transported. However, this digestive process 

 occurs not only in seeds but also in all plant regions where foods 

 are transported, and also in animals it has its likeness in the diges- 

 tive process by which foods are made soluble, so that they can 

 pass through the walls of the ahmentary canal to the blood, which 

 carries them in solution throughout the body. Both the digestion 

 and transportation of the stored foods are quite noticeable during 

 the germination of some large seeds, as in case of Corn in which 

 the endosperm becomes watery and disappears as germination 

 proceeds, or in case of Beans where the cotyledons in which the 

 food is stored gradually shrink as the young plant develops. 



The digestive process in plants as well as in animals is per- 

 formed by special substances known as enzymes, which in case of 

 the seed are secretions of the embryo. Enzymes occur in solu- 

 tion, either dissolved in water or in protoplasm, in all parts of the 

 plant where they either initiate or hasten chemical changes. 

 They are exceedingly important substances because upon them 

 the majority of chemical changes in plants depend. They are 

 specific in their action, that is, as a rule, each enzyme acts on only 

 one kind of a substance, and is concerned with only one or two 



