CHAP, i The Cell 189 



revived in 1873 the old view of an agglutinating material 

 of gelatinous nature intercalated between the radial rows 

 of the generating cells. He held, however, that it arises 

 from a decomposition of the original cell wall. 



Further light was thrown upon the problem by researches 

 made a little later on the pectosic compounds by Mangin. 

 Published in 1892 and 1893, these were of the first impor- 

 tance. Before their appearance the whole group of the 

 pectic compounds was ill-defined, and nothing was known 

 very definitely as to the distribution of most of them in the 

 cell wall. 



Mangin arranged these substances in two series, the 

 members of the first being bodies of a neutral reaction, 

 while those of the other are weak acids. In each series 

 there are several members, which show among them every 

 stage of physical condition between absolute insolubility 

 and complete solubility in water, the intermediate bodies 

 exhibiting gelatinous stages, characterized by the power of 

 absorbing water in greater or less degree. 



Of the neutral series, the two extremes are presented by 

 Pectose and Pectine. The former is insoluble in water and 

 closely associated with cellulose in the substance of the 

 membranes ; the latter is soluble in water and forms a jelly 

 with more or less facility. 



In the acid series the two most noteworthy members 

 are Pectic and Metapectic acids. The former generally exists 

 in the membrane in combination with the metals of the 

 alkaline earths, especially calcium ; when in the free state 

 it is insoluble in water. Metapectic acid is soluble in water, 

 forming a jelly. The two series are closely related to each 

 other, for by the action of heat, acids, and alkalies the 

 various members of both can be prepared from pectose. 

 The final product of the action of the reagents is the freely 

 soluble metapectic acid. 



Their reactions, as given by Mangin, show that these 



