Chap, iv.] of the Ccll-t issue in Plants after 1845, 34 I 



instead of doing so were moulded by the ideas current before 

 1845. ^ nas been shown in the preceding chapter how von 

 Mohl gradually restricted the theory of intercellular substance 

 which he had proposed in 1836, and had come in 1850 to regard 

 this substance as only a cement which might in many cases be 

 perceived between the cell-walls. It should be added here, 

 that Schleiden in connection with his theory of cells considered 

 both the intercellular substance and the cuticle to be supple- 

 mentary secretions from the cells, and made the former fill the 

 intercellular spaces, just as laticiferous and resin iferous passages 

 are filled with secretions from the adjacent cells (1845). Unger 

 too in 1855 (' Anatomie und Physiologie der Pflanzen ') thought 

 the existence of a cement between the cells necessary to pre- 

 vent their falling asunder. Schacht,, who in his ' Pflanzenzelle ' 

 of 1852 had followed Schleiden in explaining the intercellular 

 substance and the cuticle as secretions or excreta from the cells 

 of the plant, still kept on the whole to this view in 1858, 

 though he modified it in some important points. This theory 

 of Schleiden and Schacht was first opposed by Wigand in a 

 series of essays (1 850-1 861), in which in strict adherence to 

 von Mohl's theory of apposition he sought to prove, that the 

 layers which are visible in wood-cells as intermediate laminae 

 in the partition-walls, and which till then had been regarded as 

 a cement between contiguous cells, an intercellular substance, 

 were nothing else than the thin primary membranous laminae 

 formed in the process of cell-division, and subjected to subse- 

 quent chemical change, while the secondary layers of thickening 

 in von Mohl's sense lie on both sides of them. The cuticle 

 on the epidermis was explained in a corresponding manner. 

 Though Sanio in 1863 raised a variety of objections to Wigand's 

 view, he still adhered to it in principle, and found a strong 

 firmation of it in the fact, that he succeeded in producing the 

 well-known cellulose-reaction in the intercellular substance of 

 wood-cells when freed from foreign admixtures. 



The researches of Wigand and Sanio were sufficient to over- 



