no The Living Plant 



majority of the human race, — are composed almost wholly of 

 starch. 



Chemically, starch has the fornmla (CgHjoOg)??. It is formed 

 apparently thus, — from dextrose, C6H12O0, water, H2O, is with- 

 drawn, leaving CgHioOs; this substance does not occur in this 

 form in the plant, but the molecules immediately aggregate them- 

 selves (chemically, polymerize), to a considerable but unknown 

 number, expressed by the letter n, into compound molecules. 

 Starch is made up in this w^ay from dextrose, and it is of interest 

 to note that a corresponding substance made from fructose occurs 

 as a reserve food dissolved in the sap of the swollen roots of some 

 Composite plants, where it is called inulin. The formation of 

 starch has never been effected artificially outside of plants, and 

 in them it takes place only inside of those living protoplasmic 

 bodies called plastids, which include chlorophyll grains and which 

 are to be described more fully in the next chapter. The re- 

 conversion of starch to dextrose is effected through the action of 

 diastase, — one of those remarkable chemical agents called en- 

 zymes, which we are presently to study; and this is exactly what 

 happens in the digestion of starch in both the plant and animal 

 body. Indeed, this digestion can be carried on experimentally 

 and very easily in a test-tube by action of diastase bought from 

 any chemical supply company, the disappearance of the starch 

 being proven by use of the iodine. 



A fact of another kind about starch should be noticed at this 

 place. Even to the unaided eye it looks granular in texture, while 

 the microscope shows that it really is composed of definite grains, 

 which, moreover, display a remarkable structure. If a section 

 be cut from the interior of a potato, for instance, and magnified, 

 the cells are found to present an aspect well shown in the typical 

 example here pictured, (figure 34). Within each cell are numerous 

 solid grains, various in details of their shapes, but all possessing 

 in common a focal spot near the smaller end, around which are 

 excentrically-arranged layers (figures 34 and 35). Starches from 



