PECTIN, ETC. 91 



fluid. 1 An alkaline solution of nitrate of silver 

 (i : 10,000) gives a black color with tannin (p. 41). 



PECTIN 



Often replaces the intercellular substance or cer- 

 tain layers of the cell-wall. It is recognized by the 

 swelling of these layers in hot water and alkalies, 

 and their solubility in the latter as well as in con- 

 centrated oxalic acid (p. 24). With cuprammonia 

 (p. 15), pectate of copper is formed, and in thin sec- 

 tions this remains after the complete solution of 

 the other parts of the wall. 



ASPARAGIN 



Is insoluble in absolute alcohol or a concentrated 

 solution of itself, but soluble in water. On drying 

 sections which contain it or treating them with 

 absolute alcohol, acicular crystals of asparagin 

 form in the cells or the fluid about them (p. 45). 



CRYSTALLOIDS * 



Is a name used to designate protein bodies hav- 

 ing a crystalline form. They are characterized 



1 Hohiiel (Die Gerberrinden, Berlin, 1880) gives more particular 

 information as to tannin in its technical bearings. The very characteristic 

 reaction of a decoction of galls with iron was known to Pliny, and was used 

 by the ancients to detect the adulteration of verdigris with sulphate of iron 

 the oldest chemical reaction. 



* A. Schimper: Untersuchungen iiber die Proteinkrystalloide d 



