Formwechsel,sippenspezifischer Paarungsmodus und Systematik bei einigen pennaten Diatomeen

Cymbella cesatii var.paradoxa, var. nova, is significantly characterized by its total variation of size, by the size of gamete mother cells and auxospores; moreover its particular mode of pairing is significant too. Whilst in var.cesatii, in connection with its naviculoid cell shape, the combinations ventral-ventral, dorsal-dorsal, ventral-dorsal are realized haphazardly, in var.paradoxa, which is naviculoid-shaped just the same, regularly only the combination dorsal-dorsal is practicable. With regard to the naviculoid shape of the cells it is concluded that not space-mechanical causes alone are involved, but that a factor controlling the mode of pairing is at work. In comparison with the twocesatii sibs it is remarkable that inCymbella microcephala, although its cells are more strongly dorsiventrally organized, nevertheless the three combinations are realized haphazardly. On the contrary, inC. delicatula, whilst its cells are not more dorsiventrally organized, pairing always is accomplished at the ventral sides. This comparison also shows the effectiveness of factors other than the form of the partner cells. Some specific peculiarities of pairing behavior in other allogamous diatoms are compared and discussed. — In both sibs ofC. cesatii ± deformed parthenogenetic primary cells exceptionally arise. A survey demonstrates the common occurence of clearly separable infraspecific sibs and aggregates in diatoms.