ALTERNATION OF GENERATIONS 



27 



nuclear membrane, the chromatin in each falls together in little 

 masses, the nucleolus lying by the side, of the mass ; these thou 

 separate, a spindle is formed with an equatorial plate and the 

 chromatin masses pass at different rates towards the poles. 

 The nucleoli then disappear, and four chromatin balls are 

 formed which are the daughter nuclei. Only after this is com- 

 pleted, do they separate into two pairs, and the formation of a 

 cell-wall begins (Dittschlag). 



The Alternation of Generations. 



Assuming, as we are now justified in doing, the truth of the 

 foregoing ideas, we may represent the alternation of genera- 

 tions in a typical Uredine by the following diagram : 



teleutospore 



basidiospores 



uredospore. 



SPOKOPHYTE 



(2n generation) 



uredospore^ 



ascidiospore" 

 intercalary cell' 



GAMETOPHYTE 



(n generation) 



spermatium 

 $ gamete 



? gametes 



fusion-cell 



The n generation is that in which the nucleus has the 

 haploid number of chromosomes or, if there are no distinct 

 chromosomes visible, the single amount of chromatin ; in the 

 2/; generation each cell has the double (diploid) number of 

 chromosomes or the double amount of chromatin, at first sur- 

 rounded by two nuclear membranes, afterwards by one. 



