390 H. von Mohl on the Cambium-layer 



secondary cells in the parent-cells, so that a linear disposition 

 of the secondary cells in the parent-cells in the long axis of the 

 stein lays the foundation of an elongated internode — an arrange- 

 ment agreeing with the angles of a tetrahedron (sic ?), of an un- 

 developed internode — and an arrangement in a plane standing 

 perpendicularly to the axis forms an internode greatly developed 

 in breadth ; 2ndly, on the form of the process itself, this ceasing 

 at certain places sooner than in others. 



In the second stage of the process of cell-development, the 

 general uniform expansion of the cells formed in the previous 

 stage can alone act ; in this period, therefore, the volume may 

 alter, but not the form and relations. 



In the third stage, the expansion of the existing cells is the 

 exclusive influence in determining form. 



This distinction of three stages is retained in the later editions 

 of the same work (3rd ed. ii. p. 132), and the cambium (cambial 

 layer, formative layer, p. 153) is specially defined as a cellular 

 tissue which has not yet ceased to form new cells, which, accord- 

 ing to the passages above referred to, would be limited to the 

 first stage. 



It will not be superfluous, before going further, to examine 

 this conception of the cambium a little in detail. I leave out of 

 the question the circumstance that examination made with any 

 care shows that the youngest cellular tissue never forms an even 

 apparently homogeneous pultaceous mass, but that its composi- 

 tion of cells is always clearly perceptible — so that the observer 

 can find no distinction between the first and second stages ; and 

 the further circumstances, that the cells of vegetative organs are 

 multiplied by division, and not by free-cell-formation, and that 

 the intercellular passages do not become visible in consequence 

 of the fluid contained in them being replaced by air, but from the 

 cells, which in the cambium-layer are connected together as far 

 as their extreme angles, subsequently separating from each other 

 at the angles, which become rounded-off. A more important cir- 

 cumstance is, that the multiplication of cells occurs not merely in 

 the period which Schleiden calls the first stage, but also in the 

 second, and very often in the third : consequently, that division 

 into stages, attempted by Schleiden, cannot be carried out; and 

 the assertion that all elementary organs originate in the first 

 stage of cell-development of an organ, and that the subsequent 

 development of the latter depends simply upon growth of the 

 cells, is decidedly incorrect. 



I believe that, in the examination of a young organ, we may 

 distinguish three stages of cell-development ; but these must be 

 differently defined. The youngest and most rudimentary parts 

 are composed of parenchymatous cells closely applied together 



