TEMPORARY MOUNTS AND MICROCHEMICAL TESTS 85 



Pectin is not at all confined to the middle lamella, but is found in 

 other membranes, particularly in spore coats. 



Cellulose. — In concentrated sulphuric acid cellulose swells and 

 finally dissolves. It is also soluble in cuprammonia. The cuprammonia 

 can be prepared by pouring 15 per cent ammonia water upon copper 

 turnings or filings. Let the solution stand in an open bottle. It does 

 not keep well, but its efficiency is readily tested. Cotton dissolves al- 

 most immediately as long as the solution is fit for use. 



With iodine and sulphuric acid, cellulose turns blue. Treat first 

 with the undiluted iodine-potassium-iodide solution described in the 

 test for starch, then add a mixture of two parts of concentrated sul- 

 phuric acid and one part of water. 



With chloroTodide of zinc, cellulose turns violet. Dissolve commer- 

 cial chloroiodide of zinc in about its own weight of water and add 

 enough metallic iodine to give the solution a deep brown color. 



The cell walls of fungi consist oi fungus cellulose. When young, they 

 give a typical cellulose reaction ; when older, they become insoluble in 

 cuprammonia and, with iodine and sulphuric acid, show only a yellow 

 or brown, instead of the typical blue. With chloroiodide of zinc, the 

 wall stains yellow or brown, instead of violet. 



Reserve cellulose, which is common in thick- walled endosperm of 

 seeds, shows the same microchemical reactions as ordinary cellulose. 



Callose. — The thickening on the sieve plate differs from cellulose in 

 its staining reactions, and in its solubility. It is insoluble in cupram- 

 monia, but will dissolve in a 1 per cent solution of caustic soda. 



Stain in a 4 per cent aqueous solution of soda (Na2C03) for 10 

 minutes, and transfer to glycerin. The callus should take a bright red. 

 If stained very deeply and then transferred to a 4 per cent soda (with- 

 out the corallin), the stain is extracted from the cellulose but remains 

 in the callus. Unfortunately, the preparations are not permanent. 



If stained for about an hour in a dilute aqueous solution of anilin 

 blue, the stain may be extracted with glycerin until it remains only in 

 the callus. After the blue is satisfactory, a few minutes in aqueous 

 eosin will afford a good contrast. The preparation may be mounted in 

 balsam and is fairly permanent. 



Lignin. — Lignified walls are insoluble in cuprammonia. The iodine 

 and sulphuric acid or the chloroiodide of zinc, used as in testing for 

 cellulose, give the lignified walls a yellow or brown color. After a treat- 



