A uxospore formation 



109 



and the significance of this tetrad-division, which precedes conjugation, may 

 lie in the reduction of chromosomes. 



There yet remains much work to be done on the cytology of auxospore- 

 formation, as most of our present knowledge is based upon a few isolated 



cases. 



Rt 



Fig. 79. Conjugation of Rhopalodia gibba (Kiitz.) 0. Mull. The conjugating cells are seen in 

 the valve view except in fig. 3, in which they are seen in an oblique girdle view, k, nucleus ; 

 kk, small nucleus ; gk, large nucleus ; py, pyrenoid ; #, gelatinous investment. (From 

 Oltmanns, after Klebahn.) 



Karsten has stated that the type of auxospore-formation which occurs 

 in the greater number of ground species is that in which two auxospores are 

 formed by conjugation (the fifth type described above), but the observations 

 of those who have spent many years in the investigation of freshwater and 

 littoral diatoms scarcely support this statement, whereas there is much 



