68 BOTANICAL MICROTECHNIQUE. 



have partly the glandular form and are partly more or less 

 regularly formed sphaerocrystals. They are soluble in cold 

 water with difficulty, but more easily so in hot water. They 

 are also hardly soluble in acetic acid, but readily so in 

 mineral acids, in sulphuric acid without the formation of 

 gypsum needles. Ammonium carbonate gave no precipitate 

 with them, but the ammoniacal solution of ammonium 

 chloride and sodium phosphate produced a crystalline pre- 

 cipitate. The phosphoric acid was recognized with ammo- 

 nium molybdate (cf. 77, i). 



14. Iron, Fe. 



102. Weiss and Wiesner (I) have shown microchemically 

 that iron incrusts especially the thicker cell-membranes of 

 the higher plants in the form of insoluble ferric and ferrous 

 compounds, and that it also occurs in the contents of the 

 cells. The authors mentioned used as a reagent an alco- 

 holic solution of potassium sulphocyanide added directly to 

 sections cut with a silver or platinum knife. If a red color 

 appears at once, it shows the presence of a soluble ferric 

 compound ; but if it appears only after the addition of hy- 

 drochloric acid, the presence of a ferric compound insoluble 

 in water is shown. In the same way sections were treated 

 with potassium sulphocyanide and chlorine-water or nitric 

 acid to demonstrate soluble or insoluble ferrous compounds. 



Large quantities of iron compounds also occur as incrus- 

 tations of the membrane in various Schizomycetes (Clado- 

 thrix, Crenothrix, etc.) and in Closterinm. It also forms 

 thick crusts, in the form of ferric hydroxide, on the mem- 

 branes of many Confervacece (cf. Hanstein I). For the 

 microchemical recognition of iron, a 10$ solution of potas- 

 sium ferrocyanide, to which a little hydrochloric acid is 

 added, may be used in these cases. The reagent causes 

 the immediate formation of Berlin blue in the presence of 

 ferric oxide. The presence of ferrous oxide may be recog- 

 nized in the same way by the use of potassium ferricyanide.* 



* A method for the recognition of organically combined iron, the so- 

 called " masked iron," has been given by Molisch (VII). But the same 



