THE RESERVE MATERIALS OF PLANTS. 481 



is that the two members of each merge into one another 

 very gradually ; in fact, each series suggests several different 

 substances, presenting a number of gradations from 

 absolute insolubility in water to complete solubility, through 

 gelatinous states characterised by the power of absorbing 

 different quantities of water, and showing various degrees 

 of swelling in consequence. 



The neutral series includes pectose proper, which is the 

 body associated most generally in cell wall with cellulose. 

 It is not found in such cell walls as have been modified 

 by incrustation or impregnation with lignin or suberin. 

 It is insoluble in water or in ammonia-cupric oxide, by 

 which reagent it can be separated from cellulose. 



The second body of this group is pectine, which is soluble 

 in water and readily forms a jelly. It swells up at once on 

 the addition of water, yielding a viscid liquid, which filters 

 with difficulty and speedily gelatinises. This seems to be 

 the body Fremy found in many ripe fruits ; Mangin has 

 detected it in many of the so-called mucilages. 



The acid series includes two forms, of which the first is 

 described as pectic acid. This is very insoluble ; it is found 

 in the tissues usually combined with alkaline earthy bases, 

 forming often pectate of calcium. The second, the most 

 stable of them all, is metapectic acid, is soluble in water, 

 but is capable of gelatinisation. 



The two series are closely related to each other ; under 

 the action of heat, acids, and alkalis, we can, starting from 

 pectose obtain all the neutral and acid intermediate bodies 

 up to metapectic acid. 



Pectose is the most unstable ; the chemical reagents used 

 to prepare it easily transform it either into pectine or into 

 pectic acid. Even the ammonio-cupric oxide solution used 

 to separate it from cellulose rapidly effects the transforma- 

 tion of part of it. 



Pectine can be prepared in quantity from the roots of 

 the carrot. The most satisfactory method of procuring it 

 has been described by Bertrand and Malliose (43). The 

 pulp of the carrots is pressed and boiled for fifteen minutes 

 to free it from the enzyme which sets up gelatinisation, and 



