134 TEXTBOOK OF BOTANY 



sorghum) plastids containing dextrin can be found in all stages of 

 growth. Some of these dextrin-filled plastids may occur along with starch 

 grains in the ripe seeds. 



When starch grains are heated for a short time thev are transformed 

 to grains of dextrin, and become red instead of blue when treated with 

 a solution of iodine. Commercial dextrin is prepared bv subjecting starch 

 to heat. 



Glycogen and inulin. Glycogen, like starch, is a condensation 

 product of glucose. It is common in the animal kingdom, but among 

 plants it is known to occur onlv in certain fungi, bacteria and 

 algae. 



Inulin is a condensation product of fructose, and occurs in several 

 kinds of plants. If roots of salsify or dandelion are placed in 70 per cent 

 alcohol for a time, most of the inulin in them crystallizes; but the clusters 

 of crystals, though they are large, are often difficult to see because of their 

 transparency. The accumulated food in Jerusalem artichoke and oyster 

 plant is largely inulin. 



Sugars, starches, dextrins, glycogen, and inulin all belong to the gen- 

 eral class of compounds known as carbohydrates, i.e., compounds of 

 carbon, hydrogen, and oxygen in which the proportion of hydrogen to 

 oxygen is 2:1, as it is in water. 



The transformation of carbohydrates by condensation and digestion. 

 The formation of starch from sugar by chemical condensation and the 

 subsequent digestion of starch to sugar are common processes in plants. 

 All complex carbohydrates, such as starches, glycogen, inulin, cellulose, 

 and hemicelluloses, are formed from simple sugars by chemical condensa- 

 tion. Moreover, during the formation of fats, oils, proteins, and many 

 other compounds in cells, chemical condensation usually occurs at one 

 or more stages in the process. Chemical condensation occurs in every 

 living cell of both plants and animals. It is the converse of all ordinary 

 processes of digestion. Evidently a clear concept of its fundamental 

 features is necessary to the understanding of many biological processes. 

 A few examples will be given. 



When 2 molecules of a simple sugar, like glucose, unite bv condensa- 

 tion, the resultant sugar is called a disaccharide ( double sugar ) : 



Simple sugar > Water + Disaccharide 



2 C6Hi20e > H2O + C12H22O11 



