i88 The Anatomy of Plants BOOKII 



on each side of it consist only of cellulose. He noted that 

 the middle lamella thickens as the cells get older, and 

 interpreted this to mean that a transformation of the 

 substance of the cellulose into pectose takes place. 



Vogl wrote on the same subject and to much the same 

 effect in the same year. His experiments were made chiefly 

 on the roots of the dandelion and of a species of Podo- 

 spermum. He found the cellulose compounds to be in 

 greatest evidence on the internal face of the membrane 

 and the middle lamella to be mainly pectosic in nature, 

 the two gradually blending in the intermediate substance 

 of the wall. He, like Kabsch, took the view that the 

 substance gradually changes as it gets older. 



In 1864 Wiesner gave the support of his name to the 

 formation of the pectosic component from cellulose, but 

 he went further and said, that while in cortical cells the 

 change goes no further than this, it is different in corky 

 and woody cells where lignin and suberin are the ultimate 

 products of the chemical transformation. 



The nature of the middle lamella and its relation to the 

 two constituent substances was the subject of investiga- 

 tion before 1860, and the earlier views were subsequently 

 the subject of keen scrutiny. At the date mentioned it 

 was held by some writers to be a kind of intercellular 

 substance joining cells together by a kind of agglutination. 

 Other writers, among them Naegeli, held it to be the first- 

 formed layer or primary membrane of the wall. In its 

 composition the pectates were held to take a considerable 

 share, indeed Payen had pronounced it to be a mixture 

 of metallic pectates, principally those of calcium and 

 potassium. 



As we have seen, several writers immediately after 1860 

 tried to show it to be gradually differentiated from the 

 thickening wall, and hence to be quite a different thing 

 from the primary membrane. Sanio, on the other hand, 



