DEVELOPMENT AND STRUCTURE OF THE S\VARM- 



SPORES OF HYDRODiCTYON. 



HAMILTON GKEE^'WOOD TIMEEELAKE^ M. S. 

 Instructor in Botany, University of Wisconsin. 



Of the various large groups of plants the green Algae, with the 

 possible exception of Spirogyra, have perhaps been the least in- 

 vestigated from the modern standpoint of cell structure and by 

 aid of the newer technique. The special problems that need 

 careful attention are connected with the method of cell division, 

 the structure and division of the nuclei and the development 

 and structure of the swarm spores. 



Until very recently the prevailing accounts of cell division 

 accompanying spore formation in many of the coenocytic Fun- 

 gi and green Algae agi-eed that the protoplasm is divided at 

 once into uninucleate segments. But the researches of Harper 

 (11, 12) upon Synchitrium, Piloholus, Sporodinia and Fidigo 

 showed that many stages of cleavage in these forms had been 

 entirely overlooked by previous observers. Harper showed 

 that in the forms enumerated instead of the cleavage being si- 

 multaneous it is progressive in that the protoplast becomes di- 

 vided into large multinucleate masses that are further divided 

 into uninucleate ones. There is, moreover, quite a variation 

 in the manner in which this process of progressive cleavage may 

 be accomplished. It may be done by means of constriction 

 furrows in the plasma membrane alone, as for example, in 

 Sporodinia or by means of constriction furrows which fuse 

 with angular vacuoles on the inside of the protoplast as is the 

 case in Piloholus. Analogous processes may be expected to 

 occur in the spore forming cells of the coenocytic Algae. Klebs 

 (16) has, in fact, described a process of progressive cleavage 



