int. 





FIG. 46. 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\ nd 1 , I 1 } in these figures corresponds with the third 

 segment (int. nd 3 , / 3 ) shown in Fig. 46, F. 



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 (nu). 



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. 



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- 

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

 nd 2 has developed a vacuole (vac), and its nucleus has divided (comp. 

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

 nuclei (nu). 



D. nd* has divided vertically, forming a transverse plate of cells, and 

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

 of dividing, while int. nd z , shown in surface view, now contains nume- 

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



