No. 46o.] STUDIES ON PLANT CELL V. 237 



Spirogyra which'should be thoroughly investigated. Chmielew- 

 ski ('90 b) in a paper published in Russian and reviewed in the 

 Bot. Centralb., vol. 50, p. 264, 1892, described a fusion of the 

 gamete nuclei in the zygospore and an immediate mitosis, with- 

 out a period of rest, followed at once by a second division of the 

 daughter nuclei. These mitoses give the zygospore four nuclei, 

 two of which unite to form a final resting nucleus in the zygo- 

 spore while the remaining two fragment and their products 

 finally break down. This behavior offers an exception to all 

 sexual processes so far known in the plant kingdom. There are 

 some features which suggest a possible confusion with events as 

 described in the zygospore of the desmid and the auxospores of 

 certain diatoms. 



The fusion nucleus in the zygospore of Closterium and Cos- 

 marium (Klebahn, '91) divides into four at the time of germina- 

 tion and two of these break down while each of the others 

 becomes the nucleus of the two new desmids that are formed. 

 There is then in the desmids the division of the fusion nucleus 

 into four but no secondary nuclear fusions as Chmielewski 

 reports for Spirogyra. In certain diatoms, Rhopalodia (Kle- 

 bahn, '96) and Cocconeis (Karsten, : 00), there is a preliminary 

 division of the nuclei in each of the two cells which form the 

 auxospore. In Rhopalodia the mitoses are carried so far that 

 four daughter nuclei are formed in each diatom and the pro- 

 toplasm divides into two cells each of which fuses with a 

 corresponding cell of the companion pair. In both types the 

 superfluous nuclei break down so that the conjugating cells have 

 each a single functional gamete nucleus. There are then com- 

 plications in the Conjugales and the diatoms, which make nuclear 

 studies of the sexual processes exceptionally difficult and we seem 

 justified in reserving our judgment of the results of Chmielewski 

 until confirmed. It seems possible that the mitoses following the 

 germination of the zygospore in the Conjugales with the attend- 

 ant nuclear degeneration are reducing divisions in a simple and 

 primitive type of sporophyte generation but more detailed studies 

 of nuclear behavior during the formation and germination of the 

 zygospore will be necessary to settle the discussion. 



We have now finished our account of nuclear fusions in the 



