THE CELL-MEMBRANE. 347 



found it had a very wide distribution, not only in the veget- 

 able kingdom, but in the substance of the individual plant. 

 About the same time, or a little earlier, Payen (5) extracted 

 from the root of Ailanthus glandulosa a peculiar vegetable 

 jelly, which was closely related to, if not identical with, 

 Braconnot's pectic acid. 



These discoveries attracted the attention of various 

 chemists and botanists to the subject, and during the next 

 few years much was ascertained about pectic acid and its re- 

 actions. Vauquelin (6) in 1829 published an account of some 

 methods of preparing it, and of a study of its properties. 



During the next ten years, the work of Mulder (7) 

 and Fremy (8) added to our information as to the chemical 

 peculiarities of this body, and it soon appeared that it did 

 not exist alone, but that at least one other body, pec^iiie, was 

 present also. Fremy later called attention to a third similar 

 compound to which he did not at first give a name. He de- 

 scribes it as existing in fruits in the condition of a pulp, 

 and being under the action of an acid rapidly converted into 

 pectine. He distinguishes it carefully from cellulose, but 

 says he is not able to separate the two, and hazards the 

 opinion that it may be only pectine combined with a 

 certain amount of lime. Later Fremy gave it the name of 

 pectose. 



The existence of bodies of this character in bulky tissues, 

 and the possibility of their extraction by various solvents 

 having been demonstrated, attention was directed to their 

 whereabouts and their relationship to other elements of the 

 tissues. They were soon associated with the cell-membranes, 

 Mulder suggesting that though the form in which they exist 

 in different parts of the plant is not known, it is probable that 

 they are to be found in the thickening layers or depositions 

 in the cell-wall. They can be extracted by alkalies from the 

 cell-partitions. 



Payen (9) in 1846 added another contribution to our 

 knowledge by pointing out that in certain plants these 

 pectic bodies exist in combination with the metals of the 

 alkalies and alkaline earths, chietiy potassium and calcium. 

 He located these compounds chiefly in the epidermal tissues, 



