80 BOTANICAL MICROTECHNIQUE. 



sphaerocrystals of inulin are, naturally, dissolved, and the 

 spaces occupied by them appear red. 



If phloroglucin is used instead of orcin, the color produced 

 is browner. 



d. Glycogen, C,H 10 O & . 



124. Glycogen, which, according to Errera's investiga- 

 tions, is very widely distributed in the cells of fungi, is char- 

 acterized, as he has shown, by forming a colorless and 

 strongly refractive substance within the living cells, and by 

 becoming colored a deep red-brown with a .solution of 

 iodine and potassium iodide. This color disappears on warm- 

 ing to 50 or 60 C., and reappears on cooling. The gly- 

 cogen dissolves in water if the preparation is crushed 

 (Errera I). 



Since the intensity of the color produced by iodine de- 

 pends on the amount of glycogen present, by the use of 

 iodine .solutions of a given strength one may obtain some 

 quantitative estimate of the glycogen from the color. For 

 this purpose Errera (II) places the objects to be studied 

 directly in a solution containing 45 grams of water, .3 gram 

 of potassium iodide, and .1 gram of iodine. If the glycogen 

 is present in extremely small quantity, the color will be 

 orange rather than brown. Then a somewhat more con- 

 centrated solution (i : 100) may be used; but it must be 

 used very carefully. 



e. Dextrine, C 12 H 20 O 10 . 



125. Dextrine is the name given to the transition product 

 between starch and maltose. It is distinguished from the 

 latter by being insoluble in 84^ alcohol. Therefore Sachs 

 (I, 187) proposed, for the microchemical recognition of 

 dextrine, that sections of plants which showed the presence 

 of copper-reducing substances with Fehling's solution should 

 be placed in 95% alcohol for 10 to 24 hours to completely 

 dissolve out the glucose. If the copper-reaction then still 

 took place, he deduced the presence of dextrine. But, 

 according to more recent investigations, pure dextrine can- 



