I30 THE Cx^RBOHYDRATES 



action on pectic bodies which have been previously hydrolysed 

 by pectinase. 



M icrocJieuiical Reactions. 



The fact that these pectic substances are akin to cellu- 

 lose, and occur in conjunction with it, renders its identification 

 by microchemical means somewhat difficult. Mangin * more 

 particularly has investigated these matters, and gives the 

 following methods : — 



1. Methylene blue, Bismarck brown, and fuchsin stain pectic 

 substances, lignified and suberized walls, but not pure cellulose. 

 If sections thus stained are treated with alcohol, glycerine, or 

 dilute acids, the lignified or suberized walls retain their colora- 

 tion, whilst the pectic substances are decolorized with rapidity. 



2. Crocein and nigrosin stain lignified and suberized walls, 

 but do not stain pectic compounds. 



3. Crocein, naphthol black, and orseille red stain pure cellu- 

 lose, but do not stain pectic substances ; similarly, pectic com- 

 pounds are unstained by congo-red and azo-blue, whilst cellulose 

 and callose are. 



4. The middle lamella, which consists of compounds of 

 pectic acid, may be differentiated from the other pectic sub- 

 stances which are mixed with the cellulose of the cell walls by 

 the following method : A thin section is placed in a 20-25 per 

 cent solution of hydrochloric acid in alcohol for twenty-four 

 hours ; the section is then washed with water and treated with 

 methylene-blue or phenosafranin. The middle lamella stains 

 much more deeply than the rest of the wall. 



5. If, after the above treatment with acid alcohol, the sec- 

 tion be washed in a 10 per cent solution of ammonia, it is found 

 that the cells separate with ease one from the other. Accord- 

 ing to Mangin, the combined pectic acid is freed from its bases 

 by the treatment with acid alcohol, and is then dissolved by 

 the ammonia. A recombination of the pectic acid may be 

 brought about by treatment with baryta water, and after this 

 process the cells will not separate one from the other. 



6. The cellulose may be separated in the following manner : 

 A thin section is treated with cuprammonia for twenty-four 



* Mangin: " Compt. rend.," iS8g, 109, 579; iSgo, no, 295, 644. 



