34 Development of Opinion on the Nature [BOOK n. 



2. FURTHER DEVELOPMENT OF OPINION ON THE NATURE 

 OF THE SOLID FRAMEWORK OF CELL-MEMBRANE IN 

 PLANTS AFTER 1845. 



Between 1840 and 1850 the most eminent representatives of 

 phytotomy were chiefly engaged, as we have seen, in observing 

 the formation of vegetable cells, and in framing the true theory of 

 the subject by process of induction. It was not to be expected 

 that, while these labours were bringing year by year new things 

 to light and keeping opinion on the formation of cells in a con- 

 stant state of fluctuation, their results would lead to very 

 important changes in the theory of the solid framework of cell- 

 membrane founded by von Mohl. On the contrary, it was at 

 this time that his views such as we have seen them on the con- 

 nection of cells one with another, on the configuration of their 

 partition-walls and on their growth in thickness, attained their 

 greatest influence. His theory seemed to stand firm and 

 complete when contrasted with the unsettled state of opinion 

 respecting the origin of cells, and the question, how far it could 

 be made to agree with the new observations on the history of 

 cell-formation, was hardly raised. In the midst of the strife of 

 opinion on the latter subject appeared von Mohl's ' Vermischte 

 Schriften ' in 1845, in which his views on the structure of mature 

 vegetable tissue were produced in a series of monographs as 

 the apparently irrefragable result of his observations. And in 

 fact phytotomic research up to 1860 followed the train of 

 thought initiated by von Mohl, till at last the inadequacy of 

 his views was rendered apparent between 1858 and 1863 by 

 Nageli's new theory of growth by intussusception, and by the 

 profounder insight obtained into the nature of cell-formation. 



A sufficient proof of the correctness of these remarks is to be 

 found in the further development of the views of botanists on 

 the intercellular substance and the cuticle, which might have 

 adapted themselves before 1850 to the new theory of cells, but 



