THE MUCILAGINOUS MODIFICATION. 35 



affected. It sometimes happens, however, that the cell-wall 

 acquires wholly new relations to water, and becomes capable of 

 absorbing a large amount of it with great increase of volume and 

 translucency. A cell-wall which has undergone this mucilagi- 

 nous modification takes on, when placed in water, the consist- 

 ence of soft gelatin, and if the mass is then warmed it appears 

 to dissolve, forming a thick mucilage. Upon drying, the muci- 

 lage hardens into a translucent gum, in which the cellulose char- 

 acter is nearly or wholly lost. 



148. Generally the changes produced in such a wall by water 

 are so rapid that it is desirable to place the specimen at first in 

 alcohol, and then to replace this medium cautiously by water or 

 by dilute glycerin, when the variations in shape, size, and con- 

 sistence can be easily followed. The addition of alcohol will of 

 course arrest the changes at an}- stage desired. 



149. These changes can be easily traced in the outer cells of 

 the integument of a flax-seed. The mucilage appears as an 

 obscurely stratified mass nearly filling the cells, except at their 

 centre, where there is a low-arched cavity. On the cautious 



pectates are formed. These are readily decomposed by hydrochloric acid, and 

 insoluble gelatinous pectic acid is thrown down. 



Cellulose and its isomers agree in being soluble in concentrated sulphuric 

 acid, but they differ in the following points : Cellulose dissolves at once in 

 cuprammonia ; paracellulose, only after the action of acids ; metacellulose, not 

 even then. 



Vasculose is not easily soluble in concentrated sulphuric acid, but after the 

 action of oxidizing agents gives rise to resinous acids, which are separable by 

 alkalies from associated cellulose. 



Cntose, the transparent film covering the aerial organs of plants, is dissolved 

 neither by concentrated sulphuric acid nor by cupraminonia, but dissolves 

 without change in alkaline liquids. The following results of analyses by Fremy 

 and Urbain (Ann. Sc. nat. bot., 1882) show approximately the amount of 

 these substances in different parts of certain plants. 



Root of Paulmcnia. (1) Substances soluble in water and in dilute alkalies : 

 cork 45, soft bast 56, body of root 47. (2) Vasculose : cork 44, soft bast 34, 

 body of root 17. (3) Paracellulose : cork 4, soft bast 4, body of root 30. 



Stems. Vasculose increases in amount with the density of the wood. The 

 pith contains : of cellulose 37, paracellulose 38, vasculose 25 per cent. Cork 

 contains : matters soluble in acids and alkalies 5, cutose 43, vasculose 29, 

 cellulose and paracellulose 12 per cent (cutose and vasculose forming together 

 the suberine of Chevreul). 



Leaves of Ivy. Water and substances soluble in neutral solvents 707.7, 

 parenchyma (formed of cellulose and pectose) 240, fibres and vessels (of vascu- 

 lose and paracellulose) 17.3, epidermis (cutose and paracvllulose) 35 parts. 



Petals of Dahlia,. Water and soluble matters 961.30, parenchyma (of cel- 

 lulose and pectose) 31.63, vasculose 1.20, paracellulose 2.27, cutose 3.60 parts. 



