1 8 MICRO-CHEMICAL REAGENTS. 



with potassic chlorate, is a good test for suberin. 1 

 To obtain this so-called eerie reaction, thin sec- 

 tions of the tissue are treated with the reagent. 

 If suberin is present, after the solution of the 

 other parts of the cell-wall, yellow or spherical 

 masses remain, which are at first granular but 

 later become homogeneous. They consist of eerie 

 acid, and are soluble in alcohol, ether, benzol, and 

 chloroform. 



Warm nitric acid, followed by ammonia, colors 

 the middle lamella (or intercellular substance) 

 yellow. 2 



Nitric acid dissolves starch grains after causing 

 them to swell greatly ; hence it may often be used 

 in a dilute condition for clearing tissues which 

 contain much starch. 



CHROMIC ACID. 



This must be free from sulphuric acid. It is 

 employed concentrated or dilute, according to cir- 

 cumstances. 3 Since it tends to form crystals in 

 the neck of the bottle in which it is kept, the 

 stopper should be coated with vaseline, or fre- 

 quently loosened by turning. 



The cell-wall swells and finally dissolves in chro- 



1 Hohnel : Sitzber. wien. Akad., 1877, Abth. I. 



2 Dippel: Das Mikroskop, II., p. 100. 



s Dippel: Struktur der Zellhiille, 1878. Sanio : Bot. Zeitung, 1860- 

 1863. Kabsch : Jahrb. wiss. Bot., III., p. 387. Na'geli : Das Mikroskop, 

 i877> p. 475- 



