Respiration, Digestion, and Fermentation. 107 



113. Digestion of cellulose — Take a number of seeds 

 from the dried dates of commerce, and put in moist soil or 

 sawdust. Germination will take place in about six weeks. 

 Two weeks later make dissections of the seeds, and compare 

 the embryo of resting seeds with the plantlet two weeks old. 

 What effect has the germination exerted on the hard cellulose 

 walls of the seed ? Cut a thin cross-section, and stain with 

 iodine. What variations from the typical reactions of cellu- 

 lose are to be seen ? What is the fate of the cellulose ? The 

 digestion of the cellulose is accomplished by means of cytase, 

 which is also secreted by parasitic plants, and used for dis- 

 solving the walls of the host. 



114. Catalase and other oxidizing enzymes. — Take 

 fresh tissues of any convenient plant and cut up finely. Put 

 the minced material in a test tube, and cover with water. 

 Add a few drops of hydrogen peroxide. The formation of 

 bubbles of oxygen will denote the presence of catalase, one 

 of the most important of the oxidizing enzymes. A familiar 

 example of the action of this substance is to be seen in the 

 browning of the exposed surfaces of apples, peaches, pears, 

 and other fleshy fruits. In some instances the presence of 

 these enzymes may be detected by moistening a cut surface 

 with a 2 per cent, solution of gum guaiacum in alcohol. If 

 oxidizing enzymes are present, the surfaces treated will turn 

 blue. 



115. Translocation of food material. — A familiar 

 example of translocation of material in the plant is to be 

 seen in leaves. Food is formed in these organs during expo- 

 sure to sunlight about ten times as fast as it may be removed 

 by diffusion. As a consequence, the surplus accumulating is 

 converted into an insoluble form as starch, in which it does 

 not affect the absorbing or dissolving power of the sap in the 

 leaves. During the night, or at any time when the leaf is not 

 exposed to light, the slow but continuous process of diffusion 



