112 



ROLE OF THE CELL NUCLEUS 



mination by short-time exposure to distilled water: the nuclei mul- 

 tiply and the cytoplasm divides. Flagellated gametes are produced 

 and escape out of the broken cyst. Copulation of the gametes is 

 quickly followed by the growth of the zygote, which soon differen- 

 tiates into rhizoid and stalk. The whole life cycle takes about 

 5 months under laboratory conditions and 1 year in nature. 



adult 

 cap 



Zygote 

 ^i^^N 2 days 



8 days 

 Fig. 36. Life cycle of Acetabiilaria meditcrrar.ea. 



One of the main results obtained by HammerUng (1934) is the 

 demonstration that unnucleated stalks survive for a very long time 

 (several months). Still more important is the fact that these enu- 

 cleate parts are capable of important regeneration, includmg the 

 formation of large-sized caps (Fig. 37, p. 121). It was concluded by 

 Hammerling, as early as 1934, that the morphogenetic capacity of 

 an enucleate part is determined by the amount of nucleus-dependent 

 morphogenetic substances stored in it; these substances are distrib- 

 uted along an anterio-posterior concentration gradient. 



