190 The Anatomy of Plants BOOKII 



pectic substances form a group quite distinct from the 

 celluloses which are known. The ease with which they are 

 altered by the reagents used for their extraction readily 

 marks them off from the latter, as do the products of their 

 oxidation. When warmed with nitric acid they give rise 

 to mucic acid, while the celluloses are oxidized by the same 

 reagent to oxalic acid. 



The pectoses are all insoluble in ammonio-sulphate of 

 copper, and are not stained blue by iodine in any combina- 

 tion. 



Mangin studied the distribution of celluloses and pectosic 

 bodies in the cell wall by means of differential staining. 

 Cellulose acts as a feeble base, and takes up, therefore, 

 acid stains, particularly those which contain nitrogen. 

 Pectosic compounds on the contrary act as acids and 

 require basic stains. 



Mangin supplemented his observations on the staining 

 of the compounds by watching the action of solvents. As 

 just stated, the celluloses dissolve with greater or less 

 readiness in ammonio-sulphate of copper. The treatment 

 must be prolonged and conducted with due precaution, 

 but Mangin found he could free the walls entirely from 

 these substances, leaving a framework staining pale yellow 

 instead of blue with iodine and phosphoric acid, and taking 

 up the basis stains which do not colour cellulose. The 

 pectic compound remaining after the action of the alkaline 

 reagent is not unchanged pectose, but has been partly 

 converted into pectic acid by the treatment. 



Mangin succeeded also in dissolving out the pectosic 

 constituent of the wall and leaving the cellulose, by boiling 

 the tissue alternately with dilute acids ancjl dilute alkalies, 

 washing well after each operation. 



By means of these methods of procedure Mangin ascer- 

 tained that in Phanerogams, Pteridophyta, and Bryophyta 

 hardly any soft tissue is devoid of pectosic substances in 



