nd? 



FIG. 45. Nitella : Vertical sections of the growing point at four 

 successive stages. The nodes (nd), internodes (int. nd), and leaf- 

 whorls (/) are all numbered in order from the proximal to the distal end 

 of the bud, the numbers corresponding in all the figures. The proximal 

 segment (int. nd l , nd 1 , I 1 } in these figures corresponds with the third 

 segment (int. nd 3 , I 3 ) shown in Fig. 44, F. 



In A, the apical cell (ap. c] is succeeded by a very rudimentary node 

 (nd 3 ) without leaves : int. nd 1 is in vertical section, showing the proto- 

 plasm (plsm], vacuole (vac\ and two nuclei (mi}. 



In B, the apical cell has divided transversely, forming a new apical 

 cell (ap. c] and a sub-apical cell (s. ap. c] : the leaves (/ 3 ) of nd 3 have 

 appeared. 



In c, the sub-apical cell has divided transversely into the proximally- 

 situated internode (int. nd*) and the distally-situated node (nd*) of a 

 new segment ; in the node the nucleus has divided preparatory to cell- 

 division. The previously formed segments have increased in size : int. 

 net 1 has developed a vacuole (vac\ and its nucleus has divided (comp. 

 int. nd 2 in A) : int. nd 1 is shown in surface view with three dividing 

 nuclei (nit}. 



In D, nd 1 has divided vertically, forming a transverse plate of cells, 

 and is now as far advanced as nd 3 in A : the nucleus of int. nd 3 is in the 

 act of dividing, while int. nd 2 , shown in surface view, now contains 

 numerous nuclei, some of them in the act of dividing. 



