78 BOTANICAL MICROTECHNIQUE. 



120. To recognize glucose in vessels, A. Fischer (V, 74) 

 placed suitable pieces from branches split through the 

 middle in a concentrated aqueous solution of cupric sul- 

 phate for five minutes, then rinsed them in water and placed 

 them in a boiling solution of Rochelle salt and caustic soda, 

 in which he let them boil for from two to five minutes. 

 The cuprous oxide is then precipitated in the cells which 

 formerly contained sugar, and the wood may be readily cut. 

 Dried wood and alcoholic material in large pieces, whose 

 old surfaces have been previously removed, may serve for 

 the reaction. 



b. Cane-sugar, Saccharose, C ia H M O n . 



121. Cane-sugar is widely distributed among plants, and 

 suitable material for study is afforded by pieces of a sugar- 

 beet. Even on gentle boiling it cannot precipitate cuprous 

 oxide from Fehling's solution ; but on longer boiling in this 

 solution, the cane-sugar becomes converted, in consequence 

 of the strongly alkaline reaction of the solution, into the 

 so-called invert-sugar, a mixture of glucose and laevulose, 

 which reduces Fehling's solution. 



For the microchemical recognition of cane-sugar, sections 

 not too thick are placed, according to Sachs (I, 187), for a 

 short time in a concentrated aqueous solution of cupric sul- 

 phate, rapidly rinsed in water, and then transferred to a 

 solution of one part potassium hydrate in one part water, 

 heated to boiling. If cane-sugar is present, there appears 

 in the cells containing it a sky-blue color which gradually 

 diffuses into the potash. A careful microscopic control of 

 this reaction is recommended, since, as Sachs states, the 

 young cell-membranes often become colored deep blue 

 under the same treatment. 



Fehlings solution may also be used for the recognition of 

 cane-sugar, which gives a blue solution with it also. For 

 the method of using it, see 119. 



c. Inulin, C 12 H 20 O 10 . 



122. Inulin is pretty readily soluble in water and occurs 

 dissolved in the cell-sap of many plants. But, since it is 



