CRYSTALS 277 



of Ficus elastica, the leaf of ivy (Hedera helix); make a 

 separate mount of each in water, and examine with the 

 high power. When the crystals are found, draw them, with 

 a view of the adjacent cells. Make a similar study of a 

 bit of thin onion skin. 



Review. — Name ten classes of contents or products of the cell. 

 Where found? Of what use? What is chlorophyll? What is its use? 

 What is assimilation (185)? Give outline of the products of cells 

 found dissolved in cell-sap. What are the uses of sugar to plants? 

 Name some kinds of sugar found in plants. Describe an experiment 

 to test for glucose. Same for cane-sugar. How may we find the oil 

 in plants? Describe an experiment for the study of gum-resin. Why 

 does the juice containing it appear white? Describe starch grains of 

 potato. Tell how starch grains of other plants studied differ from 

 those of potato. What are the uses of starch to the plant? Where 

 is the plant's starch factory? Describe an experiment to test for starch. 

 Name some plants in which one may find amylo-dextrine. How does 

 its test differ from that for starch? What are aleurone grains? In 

 what cells are they found in kernels of wheat? Name some of the forms 

 in which we find true crystals in plant cells. 



Note. — The digestion of starch is produced by means of enzyms 

 (183) or unorganized ferments (i.e., ferments that are not bacterial 

 or fungal, but are chemical substances). These ferments, as diastase, 

 are present in seeds and other living tissues containing starch. During 

 dormant periods the enzyms either are not present, or their action is 

 prohibited by the presence of other substances. There are various 

 specific enzyms, each producing definite chemical changes. 



Grape-sugar and its associate, fruit-sugar, appear to be the forms 

 most generally useful to plants. Cane-sugar is readily inverted into 

 these sugars. 



