i82 BOTANY AND PHARMACOGNOSY. 



To this middle plate is added on either side by the newly 

 formed protoplasts a layer of substance closely resembling cellu- 

 lose, this constituting the primary membrane or primary lamella. 



Still other layers may be added, consisting of one or more of 

 the following substances : cellulose, or some modification of it ; 

 wax, silica or calcium oxalate, these layers constituting what may 

 be termed the secondary lamella. 



Cellulose in its various modifications constitutes the greater 

 proportion of the cell wall. The cellulose making up the 

 cotton fiber may be said to be the typical cellulose, and 

 is known as " cotton cellulose." It is soluble in copper ammo- 

 nium sulphate solution ; is colored blue with chlor-zinc-iodide solu- 

 tion or iodine and sulphuric acid, and is stained by acid phenolic 

 dyes, as alizarin, if previously treated with basic mordants, as 

 basic salts of aluminum, etc. 



According to their origin in the plant, or their behavior toward 

 reagents, the cellulose walls may be divided into the following 

 groups: (i) Lignocellulose walls; (2) protective cellulose walls; 

 (3) reserve cellulose walls; (4) mucilage cellulose walls, and (5) 

 mineral cellulose walls. 



Lignocellulose walls are composed of true cellulose and a 

 non-cellulose (the so-called lignin or lignone), these constituting 

 the woody (so-called lignified) portion of plants and, in some 

 instances, also the bast portion of the bark. The lignocelluloses 

 are colored yellow with chlor-zinc-iodide, or iodine and sulphuric 

 acid. On account of their containing in some instances furfurol, 

 coniferin, vanillin, cinnamic aldehyde, benzaldehyde or other alde- 

 hydic substances, they give definite color-reactions with certain 

 reagents. They are also stained by the aniline dyes, as fuchsin. 

 safranin, gentian violet, aniline blue, methylene blue. etc. 



A 2 per cent, phloroglucin solution, used in conjunction with 

 hydrochloric acid, gives a reddish-violet color with the lignocellu- 

 loses, although there are some celluloses of this class which do not 

 respond to this test, as flax (the bast fibers of Linum) ; while in 

 other plants phloroglucin may occur as a constituent of the cells. 



Aniline hydrochloride with hydrochloric acid and aniline sul- 

 phate with sulphuric acid produce a golden-yellow color in cell 

 walls containing lignocelluloses. 



