nu, 



D 



nd* 

 int.ndf 



I s 



ap.c 



B 



s.ap.c 



niv 



' } &"*&'''' i '' )' -1 ' 

 ' - *-,?/'*" i " ~~ ' 



int. nd. 1 



FIG. 47. Nitella : Vertical sections of the growing point at four 

 successive stages. The nodes (nd), internodes (int. net), 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 1 , nd 1 , / J ) in these figures corresponds with the third 

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



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

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

 plasm (plsm), vacuole (vac), and two nuclei (;/?/). 



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' A have 

 appeared. 



C, the sub-apical cell has divided transversely into the proximally- 

 situated internode (int. nd*) and the distally-situated node (nd 4 ) of a 

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

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

 nd 2 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 (nu). 



D, nd 4 has divided vertically, forming a transverse plate of cells, and 

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

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

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



