CRYSTALS, CARBOHYDRATES, AND OIL-GLOBULES. 11 



VII. CRYSTALS. 



In many of the sections already spoken of, for instance those 

 of Begonia, single crystals and clusters of crystals have at- 

 tracted attention. For a brief study of different forms of 

 crystals (see pages 52-55) the following are very serviceable : 

 petioles of Begonia, scales of onion, leaves of Tradescantia, 

 Fuchsia, and the common "Calla" (Richardia), bark of many 

 wood}' plants. 



If a thin section of the leaf of almost any Araceous plant, for 

 instance " Calla," is placed in a little water under the micro- 

 scope, it frequently happens that the discharge of acicular 

 crystals (raphides), described on page 52, can be seen without 

 difficulty. 



Apply to the specimens containing crystals the two reagents 

 spoken of in the table on page 54, and carefully note results. 



Repeat Vesque's experiment (188). 



VIII. CARBOHYDRATES DISSOLVED IN THE CELL-SAP. 



(a) Inulin (183) is deposited from its solution in cell-sap 

 whenever the cells are placed for a time in alcohol or even in 

 glycerin. Its characteristic forms are not likely to be mistaken 

 for anything else met with in the tissues. Excellent material is 

 afforded not only by the common Dahlia, but by Cichory and 

 Dandelion (see Fig. 35). 



(V) The sugars. Examine a thin section of beet-root by the 

 method described in 184. Compare with it a thin section of any 

 ripe fruit. 



IX. OTHER CELL-CONTENTS. 



Oil Globules, sometimes of large size, but generally minute, 

 are to be looked for in those seeds which do not contain starch 

 (compare 511). Examine in these the effect of ether on the par- 

 ticles of oil, and also make sections through the leaves of St. 

 John's-wort, Rue, and Dictamnus, and through the rind of an 

 orange or lemon to determine the shape of the receptacles con- 

 taining oily matters. 



Resins, etc. For a study of these, proceed as directed in 56, 

 employing .young shoots of Pine. 



Tannin, etc. For the detection of tannin, solutions of iron (see 

 59) may be used ; but the results are generally more satisfactory 

 when a solution of potassic or ammonic dichromate is employed. 

 The color imparted to the cells containing much tannin is brownish 



