THE HIGHER CRYPTOGAMIA. 241 



The first division at right angles to the free outer sur- 

 face of the cells of the second degree oiAspidium filix-mas 

 and A. spimdosum is produced sometimes by a septum 

 parallel to the front surface, i. e., the surface by which the 

 cell of the second degree is connected with the cell of the first 

 degree (PI. XXVII, tig. 2, PI. XXXII, fig. 4), and some- 

 times by a longitudinal septum meeting the front wall at an 

 angle of about 70 (PI. XXVII, fig. 1). In the former 

 case the second mode of division follows upon the first, in 

 the latter case the first mode of division follows upon the 

 second ; the final result is the same in both cases. The 

 further divisions of the cells of the terminal bud are subject 

 to not less stringent rules. The tendency to transform the 

 zigzag line of succession of the generations of cells resulting 

 from each cell of the second degree into an uniformly ascend- 

 ing spiral line, manifests itself especially in the frequent 

 occurrence of three-jointed groups of cells which originate 

 in the following manner the septum produced in a cell of 

 the outer surface is parallel to no one of the side walls, but 

 cuts two of the side walls of the mother cell which form an 

 edge, in such manner that the latter is divided into a 

 smaller daughter-cell with a three-sided outer wall, and 

 a larger cell with a four-sided outer wall. The latter cell 

 is divided again by a septum almost at right angles to 

 the one last formed. Instead of one cell of the n th 

 degree there are now three : one of the ^+i th and two 

 of ^+2 th degree. 



The cell-succession of the terminal bud, and the form of 

 the terminal cell which is possibly the result not the cause 

 of such cell-succession, are manifestations of the same power 

 of growth, by wliich the arrangement of the fronds on the 

 axis is determined. After long extended and often re- 

 peated observations of the attendant circumstances, the 

 conclusion will not be premature, that the power by which 

 the form of the growing portions of plants is determined, 

 is manifested in the details of the cell-multiplication by so 

 much the less in proportion as the organs in question are 

 composed of a greater number of cells. The main direc- 

 tions in which the cell-multiplication takes place are fixed : 

 the number however and mode of succession of the cell- 



16 



