140 



MORPHOLOGY OF TISSUES. 



last is again immediately broken up by a septum {11", IP) into two disc-shaped 

 cells, and in each of these numerous small cells arise by the formation of vertical 

 and afterwards horizontal walls (as may be seen in the figure further back from 

 the apex); and it is easily seen how the whole branch is built up of portions 

 of tissue, each of which originated from a single segment. The same takes place 



Fig. 109.— Apical region of a shoot oi Metzgeriafurcata in the act of bifurcation, looked at from tlie surface {after Kny). 

 The shoots consist of a single layer of cells (ff), which is however penetrated by a mid-rib n n', three to six layers in 

 thiclcness. 



in the lateral branchlets x, y, which in this case arise originally from lateral 

 protuberances of the apical cell. These processes are remarkably clearly seen 

 in Stypocaulon, in the first place because only one row of segments is formed 

 lying one over another, and in the second place because the segments themselves 

 are transformed into portions of tissue without at the same time growing, as is 



Fig. 110.— Diagrammatic representation of the segmentation of the apical cell, and of the first divisions in the segment of 

 Metxgeriafurcata (after Kny). A apex seen from the surface ; B the same in vertical longitudinal section ; C an apex in the 

 act of bifurcation ; a new apical cell is formed in the third-youngest segment. 



usually the case. Distortions often occur from the growth of the segments, which 

 render difficult an investigation of the processes of division. 



Figs. 109 and no show us a case in which the apical cell is divided alternately 

 right and left by oblique walls, so as to produce two rows of segments attached 

 to one another in a zigzag manner within and behind, but separated to some 



