Chap, hi.] of Cell-membrane in Plants. 293 



tion of visible structure must not be disturbed by physiological 

 views ; he used therefore his thorough physiological knowledge 

 chiefly to give a more definite direction to his anatomical 

 researches, and to illustrate the connection between structure 

 and function in organs. By scarcely any other phytotomist 

 was the true relation between physiological and anatomical 

 research so well understood and turned to such practical 

 account as by von Mohl, who was equally averse to the entire 

 separation of phytotomy from physiology, and to the undue 

 mixing up of the one with the other, which had led his 

 predecessors, Meyen especially, into misconceptions. 



His anatomical researches profited by his extraordinary 

 technical knowledge of the microscope ; he could himself 

 polish and set lenses, which would bear comparison with the 

 best of their time. As the majority of botanists from 1830 to 

 1850 had little knowledge of the kind, there was no one so 

 well qualified as von Mohl to give instruction in short treatises on 

 the practical advantages of a particular instrument, to remove 

 prejudices, and finally as in his ' Mikrographie ' (1846) to give 

 detailed directions for the management of the instrument. 



But his mental endowments were of course of the higher 

 importance, and it is difficult to imagine any more happily 

 suited to the requirements of vegetable anatomy during the 

 period from 1830 to 1850. At a time when men were building 

 fanciful theories on inexact observations, when Gaudichaud was 

 once more explaining the growth in thickness of the woody 

 portions of the plant after the manner of Wolff and Du Petit- 

 Thouars, when Desfontaines' account of the endogenous and 

 exogenous growth of stems was still accepted, when Mirbel was 

 endeavouring to support his old theory of the formation of 

 cells by new observations and beautiful figures, when Schulz 

 Schulzenstein's wildest notions respecting laticiferous vessels 

 were being rewarded with a prize by the Paris Academy, when 

 Schleiden's hastily adopted views respecting cells and fertilisa- 

 tion appeared on the scene with great external success, von 



