chap, in.] of Cell-membrane in Plants. %h\ 



the settlement of the questions taken up at the commencement 

 of the century. Moreover after 1840, with the appearance o\ 

 Schleiden and Nageli on the scene, new points of view were 

 suddenly disclosed, and new aims were proposed in phytotomic 

 investigation ; it is no objection to this view of the subject, that 

 the most productive portion of von Mohl's labours falls in the 

 succeeding twenty years, and that during this later period his 

 position is one of equal authority with the new tendency and 

 of participation in it. Up to 1845 ms discoveries were the 

 culminating point of the older phytotomy ; they put the finish- 

 ing stroke to the work which Mirbel, Link, Treviranus, and 

 Moldenhawer had begun. The object almost exclusively pur- 

 sued during all this period was to frame as true a scheme as 

 possible of the inner structure of the mature organs of the 

 plant ; it was requisite to gain a right understanding of the 

 diversities of cells and forms of tissues, to classify them and 

 supply them with names, and to secure well-conceived defini- 

 tions of these names. Hence almost exclusive attention was 

 paid to the configuration of the solid framework of cell-mem- 

 brane, and of this chiefly in the matured state, to the form of 

 the several elementary organs and their combination in the 

 tissue, to the sculpture of the wall-surfaces, and to the connec- 

 tion of cell-spaces by pores or their separation by closed walls. 

 There was much discussion, especially at first, on the contents 

 of vessels and cells, and on supposed movements of sap in 

 connection with anatomical research, but there was no 

 careful connected investigation of the cell-contents ; it was not 

 yet recognised that the true living body of the vegetable cell is 

 only a definite part of the contents inclosed by the cell-wall : 

 the solid walls, the framework of the whole building, were 

 regarded as of primary importance in the structure of the cell. 

 It was not till the following period that in the light of historical 

 development another view asserted itself, namely, that the 

 solid framework of vegetable tissue with all its importance is 

 yet in the genetic sense only a secondary product of the 



